Fix various typos mostly in documentation files

Fix various typos mostly in documentation files

* OS2_MAKEFILE: Fix a typo in comment ("it is there").
* README.md: Fix typos ("is not", "gc_inline.h", "bytes from",
"processed").
* doc/README.OS2: Fix typos ("how", "linking").
* doc/README.amiga: Fix typos ("GC", "e.g.", "GC_*_typed", "i.e.",
"SMakefile.amiga", "communications").
* doc/README.cmake: Fix a typo ("go to").
* doc/README.ews4800: Fix a typo ("a unique").
* doc/README.solaris2: Fix a typo ("toolchain").
* doc/finalization.md: Fix incorrect number of markup '#' symbols to
denote H2 header.
* doc/overview.md: Likewise.
* doc/gcdescr.md: Fix typos ("collects", "then advances", "is not",
"treated by").
* doc/gcinterface.md: Fix typos ("Build it", "Allocates",
"deallocates", "forces", "Causes", "Replaces", "Registers",
"traceable_alloc", "single_client_traceable_alloc").
* doc/leak.md: Fix typos ("there is", "provides").
* doc/overview.md (Further reading): Replace "&" with "and".
* doc/porting.md: Add missing ")" symbol; add missing comma; fix typos
("region_start", "region_end", "collector's", "are needed",
"GC_save_callers").
* include/private/gc_priv.h: Fix a typo in comment ("gc_inline.h").
* os_dep.c [GWW_VDB] (detect_GetWriteWatch, GC_gww_read_dirty): Fix
abbreviation ("Win2K") in a comment.
* os_dep.c [MSWIN32] (GC_wnt): Likewise.
* os_dep.c [GWW_VDB] (GC_gww_read_dirty): Fix a typo in comment
("behavior").