Added the ability for users to create new regex commands.

To do this currently, it must be done in multi-line mode:

(lldb) commands regex --help "Help text for command" --syntax "syntax for command" <cmd-name>

Any example that would use "f" for "finish" when there are no arguments,
and "f <num>" to do a "frame select <num>" would be:
(lldb) commands regex f
Enter multiple regular expressions in the form s/find/replace/ then terminate with an empty line:
s/^$/finish/
s/([0-9]+)/frame select %1/

(lldb) f 11
frame select 12
...
(lldb) f
finish
...

Also added the string version of the OptionValue as OptionValueString.

llvm-svn: 129855