Overhaul

I see that REPL is unmaintained for quite a long time.
So I’ve decided to fix some issues and to refactor REPL.

Key features of my commits:
* Trimmed down from 105 to 51 strings,
* Fixed all issues (#14, #15, #16),
* Used optparse stdlib library,
* Made standalone installation fully workable,
* Added `-v, --version` flag,
* Added short form of flags — so you can `repl -s ruby` instead of `repl --stdin ruby`,
* Updated all documentation — both `man` and `README.md`,
* More helpful `--debug` — lists all parsed options,
* Now you can format `REPL_PROMPT`, insert `%s` where the name of program should be,
* Version is moved from `lib/repl/version.rb` to `bin/repl` so `repl` can be installed standalone,
* When installing standalone, man page installs too,
* `Makefile` added to install/uninstall standalone version (you can still stick with `curl`),
* Precompiling the pattern and just formatting it each time with `STDIN.gets.chomp` and precompiling the prompt is actually a little bit faster and cleaner.

@defunkt: if you don’t like some of my changes, just tell me and I revert it back.
I shall continue maintaining this repo if you don't mind.

To bump the version, look on line 22 of `bin/repl`.