micropython: add micropython component

components/language/micropython/docs/library/gc.rst

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+:mod:`gc` -- control the garbage collector
+==========================================
+
+.. module:: gc
+   :synopsis: control the garbage collector
+
+|see_cpython_module| :mod:`python:gc`.
+
+Functions
+---------
+
+.. function:: enable()
+
+   Enable automatic garbage collection.
+
+.. function:: disable()
+
+   Disable automatic garbage collection.  Heap memory can still be allocated,
+   and garbage collection can still be initiated manually using :meth:`gc.collect`.
+
+.. function:: collect()
+
+   Run a garbage collection.
+
+.. function:: mem_alloc()
+
+   Return the number of bytes of heap RAM that are allocated.
+
+   .. admonition:: Difference to CPython
+      :class: attention
+
+      This function is MicroPython extension.
+
+.. function:: mem_free()
+
+   Return the number of bytes of available heap RAM, or -1 if this amount
+   is not known.
+
+   .. admonition:: Difference to CPython
+      :class: attention
+
+      This function is MicroPython extension.
+
+.. function:: threshold([amount])
+
+   Set or query the additional GC allocation threshold. Normally, a collection
+   is triggered only when a new allocation cannot be satisfied, i.e. on an
+   out-of-memory (OOM) condition. If this function is called, in addition to
+   OOM, a collection will be triggered each time after *amount* bytes have been
+   allocated (in total, since the previous time such an amount of bytes
+   have been allocated). *amount* is usually specified as less than the
+   full heap size, with the intention to trigger a collection earlier than when the
+   heap becomes exhausted, and in the hope that an early collection will prevent
+   excessive memory fragmentation. This is a heuristic measure, the effect
+   of which will vary from application to application, as well as
+   the optimal value of the *amount* parameter.
+
+   Calling the function without argument will return the current value of
+   the threshold. A value of -1 means a disabled allocation threshold.
+
+   .. admonition:: Difference to CPython
+      :class: attention
+
+      This function is a MicroPython extension. CPython has a similar
+      function - ``set_threshold()``, but due to different GC
+      implementations, its signature and semantics are different.