[sync]: Document all procedures

core/sync/doc.odin

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+/*
+Synchronization primitives
+
+This package implements various synchronization primitives that can be used to
+synchronize threads' access to shared memory.
+
+To limit or control the threads' access to shared memory typically the
+following approaches are used:
+
+* Locks
+* Lock-free
+
+When using locks, sections of the code that access shared memory (also known as
+**critical sections**) are guarded by locks, allowing limited access to threads
+and blocking the execution of any other threads.
+
+In lock-free programming the data itself is organized in such a way that threads
+don't intervene much. It can be done via segmenting the data between threads,
+and/or by using atomic operations.
+*/
+package sync