Fix some formatting errors, typos and other problems (#78)

Some notes:
- Removed a TODO note that was fixed in commit 43d9fbac.
- Removed a duplicate note about the '%l' time format in the changelog.
- Applied the following documentation fixes from Terrence J. Doyle:
  - https://www.mail-archive.com/ast-developers@lists.research.att.com/msg01852.html
  - https://www.mail-archive.com/ast-developers@lists.research.att.com/msg01856.html
- Fixed strange grammar in one of the error messages.
- Added missing options for rksh to the synopsis section.
- Applied a formatting fix from ksh93v- to the man page.
- Replaced a C99 line comment in src/lib/libast/comp/realpath.c with a
  proper comment that is valid in C89.
- Prioritize UTC over GMT in the documentation (missed by commit c9634e90).
- Add some extra information for 'ksh -R file' to the man page. This patch
  is from Red Hat: https://git.centos.org/rpms/ksh/blob/c8/f/SOURCES/ksh-20080202-manfix.patch

src/cmd/INIT/release.c

@@ -43,7 +43,7 @@ USAGE_LICENSE
 "	window year of 69 (we can produce an example coding dated 1991 - this"
 "	can be patented?, how about 1+1=2?.) The date tag lines are followed by"
 "	\areadme\a text in reverse chronological order (newer entries at the"
-"	top of the file.) If no selection options are spcified then all"
+"	top of the file.) If no selection options are specified then all"
 "	changes are listed. If no \afile\a operands are specified then the"
 "	standard input is read.]"
 "[+?The entries for each \afile\a are annotated with the file directory name.]"