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/COMPATIBILITY

@@ -236,7 +236,7 @@ omitted features that are completely upward compatible.
 	the stty lnext character is set to control-v or is unset.
 	The sequence escape control-v will display the shell version.
 
-29.	In ksh-88, DEBUG traps were executed. after each command.  In ksh-93
+29.	In ksh-88, DEBUG traps were executed after each command.  In ksh-93
 	DEBUG traps are executed before each command.
 
 30.	In ksh-88, a redirection to a file name given by an empty string was