[Refactor] Use defsubst for 'inf-ruby-fix-completions-on-windows'
Store non-whitespace input in the REPL history, regardless of character length.

The former behaviour to exclude 1-2 letter inputs was rather unintuitive.
Use 'ruby-backward-sexp' instead of 'backward-sexp'

Ruby-mode doesn't customize 'forward-sexp-function', but it does have its own
forward/backward-sexp commands. With this change, you can put the point after
a class definition or after the end of a do/end block, press `C-x C-e`, and it
will send the whole definition or block to the repl.
Fix commit 'Store non-whitespace input in the REPL history, ...'
Fix commit 'Store non-whitespace input in the REPL history, ...'
[Refactor] Use 'kbd' macro for key bindings
Delete obsolete TODO comment
Added macruby to inf-ruby-implementations

Needs its own entry as macirb doesn't support the --inf-ruby-mode option
Drop --inf-ruby-mode

Closes #13
inf-ruby-mode: Modify the docstring
Move keys to a new minor mode

* Add `enh-ruby-mode` to `ruby-source-modes`.
* Hook it up in `inf-ruby-setup-keybindings`.
* Fixes #19.