change to callback style in bridge

[furushchev]

Existing bridge waits I/O with polling that consumes CPU much. New bridge instead gets I/O with callback invocation. Also includes some bugfixes:

• fix: remove ansi escape character from string on getting from remote process
• improve: support getting intermediate output / error in bridge (though they are not yet passed to client)
• improve: support simple completion (Addressing #1)
• fix: replace nil with empty string on eval (Closes #10 )
• improve: support compilation (through it does not actually compile, but just eval)