Fix some errors in the documentation and other minor issues (#42)

Somewhat notable changes in this commit:
- The 'set +r' bugfix (re: 74b41621) is now documented in the
  changelog.
- Missing options have been added to the synopsis section of the
  ksh man page.
- The minor formatting fix from https://github.com/ksh-community/ksh/pull/5
  has been applied to the ksh man page.
- A few fixes from 5e747cfb
  have been applied to the ksh man page.
- The man page fixes from https://github.com/att/ast/pull/353
  have been applied, being:
  - An addition to document the behavior of 'set -H'.
  - A fix for the cd section appending rksh93.
  - A fix for some options being indented too far.
  - Removal of a duplicate section documenting '-D'.
  - Reordering the options for 'set' in alphabetical order.
  - A minor fix for the documentation of 'ksh -i'.

src/cmd/builtin/pty.c

@@ -33,7 +33,7 @@ USAGE_LICENSE
 "[+?Input to \bpty\b will be written to the standard input of this "
     "command. The standard output and standard error from the command will "
     "be written to the standard output of \bpty\b.]"
-"[+?The \bpty\b commmand terminates when the command completes.]"
+"[+?The \bpty\b command terminates when the command completes.]"
 "[d:dialogue?Execute the dialogue on the standard input. A dialogue is a "
     "sequence of commands, one command per line. All \are\a patterns are "
     "extended regular expressions. The \are\a \b?1\b will print the subject "
@@ -58,7 +58,7 @@ USAGE_LICENSE
         "[r [\are\a]]?read a line from the master [and it should match "
             "re]]]"
         "[s \amilliseconds\a?sleep for \amilliseconds\a]"
-        "[t \amilliseconds\a?set the master read timout to "
+        "[t \amilliseconds\a?set the master read timeout to "
             "\amilliseconds\a; the default is \b1000\b]"
         "[u \are\a?read lines from the master until one matches \are\a]"
         "[v \alevel\a?set the verbose trace \alevel\a, more output for "