Typecheck files when emacs is idle

The buffer isn't saved, instead its content is sent through
the swank call
Fix parsing of Swank strings

- unescape escaped double-quotes
- parse strings with an auxiliary parser rather than a regex
(the regex would cause a stack overflow for strings over 2000 characters)
When logging Swank messages, tuncate long strings

* Now that we may pass entire buffer contents in Swank messages,
we don't want the log to become huge.
Typecheck Java files when idle
Replaced nullable strings with Some[String]
Updated documentation
Merge pull request #16 from edani/continuous-typecheck

Typecheck buffers when emacs is idle