add ota algorithm for device

1. effective "Differential Upgrade" patch algorithm with high compression rate
2. effective recovery algorithm support recovery firmware in blocks which has low memory consumption and wear-leveling strategies, especially suitable for embeded devices with low RAM.
3. add sample ota bootloader project, see:
board\TencentOS_tiny_EVB_MX_Plus\KEIL\ota\ota_bootloader_recovery
4. add sample application project for download firmware through http, see:
board\TencentOS_tiny_EVB_MX_Plus\KEIL\ota\ota_application_download_through_http
5. add sample application project for download firmware through qcloud explorer console, see:
board\TencentOS_tiny_EVB_MX_Plus\KEIL\ota\ota_application_download_through_qcloud_iot_explorer
6. an OTA markdown document is pending

components/ota/common/lzma/3rdparty/Ppmd7Dec.c

@@ -0,0 +1,191 @@
+/* Ppmd7Dec.c -- PPMdH Decoder
+2018-07-04 : Igor Pavlov : Public domain
+This code is based on PPMd var.H (2001): Dmitry Shkarin : Public domain */
+
+#include "Precomp.h"
+
+#include "Ppmd7.h"
+
+#define kTopValue (1 << 24)
+
+BoolInt Ppmd7z_RangeDec_Init(CPpmd7z_RangeDec *p)
+{
+  unsigned i;
+  p->Code = 0;
+  p->Range = 0xFFFFFFFF;
+  if (IByteIn_Read(p->Stream) != 0)
+    return False;
+  for (i = 0; i < 4; i++)
+    p->Code = (p->Code << 8) | IByteIn_Read(p->Stream);
+  return (p->Code < 0xFFFFFFFF);
+}
+
+#define GET_Ppmd7z_RangeDec CPpmd7z_RangeDec *p = CONTAINER_FROM_VTBL(pp, CPpmd7z_RangeDec, vt);
+ 
+static UInt32 Range_GetThreshold(const IPpmd7_RangeDec *pp, UInt32 total)
+{
+  GET_Ppmd7z_RangeDec
+  return p->Code / (p->Range /= total);
+}
+
+static void Range_Normalize(CPpmd7z_RangeDec *p)
+{
+  if (p->Range < kTopValue)
+  {
+    p->Code = (p->Code << 8) | IByteIn_Read(p->Stream);
+    p->Range <<= 8;
+    if (p->Range < kTopValue)
+    {
+      p->Code = (p->Code << 8) | IByteIn_Read(p->Stream);
+      p->Range <<= 8;
+    }
+  }
+}
+
+static void Range_Decode(const IPpmd7_RangeDec *pp, UInt32 start, UInt32 size)
+{
+  GET_Ppmd7z_RangeDec
+  p->Code -= start * p->Range;
+  p->Range *= size;
+  Range_Normalize(p);
+}
+
+static UInt32 Range_DecodeBit(const IPpmd7_RangeDec *pp, UInt32 size0)
+{
+  GET_Ppmd7z_RangeDec
+  UInt32 newBound = (p->Range >> 14) * size0;
+  UInt32 symbol;
+  if (p->Code < newBound)
+  {
+    symbol = 0;
+    p->Range = newBound;
+  }
+  else
+  {
+    symbol = 1;
+    p->Code -= newBound;
+    p->Range -= newBound;
+  }
+  Range_Normalize(p);
+  return symbol;
+}
+
+void Ppmd7z_RangeDec_CreateVTable(CPpmd7z_RangeDec *p)
+{
+  p->vt.GetThreshold = Range_GetThreshold;
+  p->vt.Decode = Range_Decode;
+  p->vt.DecodeBit = Range_DecodeBit;
+}
+
+
+#define MASK(sym) ((signed char *)charMask)[sym]
+
+int Ppmd7_DecodeSymbol(CPpmd7 *p, const IPpmd7_RangeDec *rc)
+{
+  size_t charMask[256 / sizeof(size_t)];
+  if (p->MinContext->NumStats != 1)
+  {
+    CPpmd_State *s = Ppmd7_GetStats(p, p->MinContext);
+    unsigned i;
+    UInt32 count, hiCnt;
+    if ((count = rc->GetThreshold(rc, p->MinContext->SummFreq)) < (hiCnt = s->Freq))
+    {
+      Byte symbol;
+      rc->Decode(rc, 0, s->Freq);
+      p->FoundState = s;
+      symbol = s->Symbol;
+      Ppmd7_Update1_0(p);
+      return symbol;
+    }
+    p->PrevSuccess = 0;
+    i = p->MinContext->NumStats - 1;
+    do
+    {
+      if ((hiCnt += (++s)->Freq) > count)
+      {
+        Byte symbol;
+        rc->Decode(rc, hiCnt - s->Freq, s->Freq);
+        p->FoundState = s;
+        symbol = s->Symbol;
+        Ppmd7_Update1(p);
+        return symbol;
+      }
+    }
+    while (--i);
+    if (count >= p->MinContext->SummFreq)
+      return -2;
+    p->HiBitsFlag = p->HB2Flag[p->FoundState->Symbol];
+    rc->Decode(rc, hiCnt, p->MinContext->SummFreq - hiCnt);
+    PPMD_SetAllBitsIn256Bytes(charMask);
+    MASK(s->Symbol) = 0;
+    i = p->MinContext->NumStats - 1;
+    do { MASK((--s)->Symbol) = 0; } while (--i);
+  }
+  else
+  {
+    UInt16 *prob = Ppmd7_GetBinSumm(p);
+    if (rc->DecodeBit(rc, *prob) == 0)
+    {
+      Byte symbol;
+      *prob = (UInt16)PPMD_UPDATE_PROB_0(*prob);
+      symbol = (p->FoundState = Ppmd7Context_OneState(p->MinContext))->Symbol;
+      Ppmd7_UpdateBin(p);
+      return symbol;
+    }
+    *prob = (UInt16)PPMD_UPDATE_PROB_1(*prob);
+    p->InitEsc = PPMD7_kExpEscape[*prob >> 10];
+    PPMD_SetAllBitsIn256Bytes(charMask);
+    MASK(Ppmd7Context_OneState(p->MinContext)->Symbol) = 0;
+    p->PrevSuccess = 0;
+  }
+  for (;;)
+  {
+    CPpmd_State *ps[256], *s;
+    UInt32 freqSum, count, hiCnt;
+    CPpmd_See *see;
+    unsigned i, num, numMasked = p->MinContext->NumStats;
+    do
+    {
+      p->OrderFall++;
+      if (!p->MinContext->Suffix)
+        return -1;
+      p->MinContext = Ppmd7_GetContext(p, p->MinContext->Suffix);
+    }
+    while (p->MinContext->NumStats == numMasked);
+    hiCnt = 0;
+    s = Ppmd7_GetStats(p, p->MinContext);
+    i = 0;
+    num = p->MinContext->NumStats - numMasked;
+    do
+    {
+      int k = (int)(MASK(s->Symbol));
+      hiCnt += (s->Freq & k);
+      ps[i] = s++;
+      i -= k;
+    }
+    while (i != num);
+    
+    see = Ppmd7_MakeEscFreq(p, numMasked, &freqSum);
+    freqSum += hiCnt;
+    count = rc->GetThreshold(rc, freqSum);
+    
+    if (count < hiCnt)
+    {
+      Byte symbol;
+      CPpmd_State **pps = ps;
+      for (hiCnt = 0; (hiCnt += (*pps)->Freq) <= count; pps++);
+      s = *pps;
+      rc->Decode(rc, hiCnt - s->Freq, s->Freq);
+      Ppmd_See_Update(see);
+      p->FoundState = s;
+      symbol = s->Symbol;
+      Ppmd7_Update2(p);
+      return symbol;
+    }
+    if (count >= freqSum)
+      return -2;
+    rc->Decode(rc, hiCnt, freqSum - hiCnt);
+    see->Summ = (UInt16)(see->Summ + freqSum);
+    do { MASK(ps[--i]->Symbol) = 0; } while (i != 0);
+  }
+}