Fix various minor problems and update the documentation (#237)

These are minor fixes I've accumulated over time. The following
changes are somewhat notable:

- Added a missing entry for 'typeset -s' to the man page.
- Add strftime(3) to the 'see also' section. This and the date(1)
  addition are meant to add onto the documentation for 'printf %T'.
- Removed the man page the entry for ksh reading $PWD/.profile on
  login. That feature was removed in commit aa7713c2.
- Added date(1) to the 'see also' section of the man page.
- Note that the 'hash' command can be used instead of 'alias -t' to
  workaround one of the caveats listed in the man page.
- Use an 'out of memory' error message rather than 'out of space'
  when memory allocation fails.
- Replaced backticks with quotes in some places for consistency.
- Added missing documentation for the %P date format.
- Added missing documentation for the printf %Q and %p formats
  (backported from ksh2020: https://github.com/att/ast/pull/1032).
- The comments that show each builtin's options have been updated.

src/cmd/ksh93/sh/path.c

@@ -1439,7 +1439,7 @@ static void exscript(Shell_t *shp,register char *path,register char *argv[],char
 
 
 /*
- * add a pathcomponent to the path search list and eliminate duplicates
+ * add a path component to the path search list and eliminate duplicates
  * and non-existing absolute paths.
  */
 static Pathcomp_t *path_addcomp(Shell_t *shp,Pathcomp_t *first, Pathcomp_t *old,const char *name, int flag)
@@ -1813,4 +1813,3 @@ void path_alias(register Namval_t *np,register Pathcomp_t *pp)
 	else
 		_nv_unset(np,0);
 }
-