Support restarting multi process programs by allowing regex in process name

[codeofpi]

With the current way of finding processes that needs to be restarted on code change, services with multiprocessing enabled are not restarted as the child processes in that case will have variable program names.

This pull request allows program and group argument to support regex input also.

for eg.

[program:abcd]
numprocs=4
numprocs_start=01
process_name=%(program_name)s_%(process_num)02d

[timakro]

Thanks for your contribution! Here's what needs to be done before I can merge this:

• The regular expression should already be re.compiled at the start and errors should be handled like this.
• Instead of combining everything into a single regular expression keep a list of compiled regular expressions and use any(compiled_regex.match(program) for compiled_regex in program_regexes). By using match intead of search you don't have to wrap the regex in ^$.
• Document that regular expressions are expected instead of plain strings in --help and update the README accordingly.

This is a breaking change in the rare case that existing PROG/GROUP params contain special regex characters.