Ensure fsautocomplete.exe is run through mono on Linux/Mac

* Run fsautocomplete.exe through mono on Linux/Mac
* Fix tests on Linux/Mac
* Rename server's public methods _read (read_line) and _read_all (read_all)
* Add 'eof' param to .read_all() for cases where EOF may be ambiguous ('help' command)
* Ensure that .read_all() always returns a JSON object even if it's a fake one ('help' command)
Fixes
Merge pull request #385 from guillermooo/st-linux-fsac

Make autocomplete daemon work on Linux/OSX