Added closing Lua state during os.exit() for Lua 5.2+ (closes #11).

This calls finalizers before exiting the process.
Cleaned trailing whitespaces.
Updated Serpent (0.272) to fix array indexes serialization.
Added check for loading 'os' module that may be absent on some systems.
Added number conversion for MOBDEBUG_PORT.

Some environments that don't support getenv return a string instead.
Added support for setting/deleting breakpoints at run-time.
Updated coroutine debugging to avoid using `require` calls.
Fixed STEP command broken by run-time breakpoint changes (fixes #12).
Updated handling of `os.getenv` that may return multiple values (fixes #13).
Added DONE command to stop debugging and continue execution.
Added `pause` method to suspend debugging from the application.
Moved closing debugging connection after responding to the controller.
Updated README for 0.56.
Fixed compatibility with Lua 5.2 (#13).
Added line mapping support for debugging Lua-based languages.
Added path processing for chunk names that look like file names.
Minor updates to README.
Fixed localizaton in breakpoint handling function.
Added support for nginx debugging using internal coroutine API.
Merge pull request #1 from pkulchenko/master

merge with upstream