Various fixes related to inclusion in MELPA

See milkypostman/melpa#922.

- Fix documentation following checkdoc rules
- Don't alter ruby-mode-hook automatically: this is bad practice.
- Add autoload cookies so 'require is not necessary when installing from package
- Remove redundant code relating to minor mode
- Declare keymap as a documented variable
- Use forward-line in place of next-line, which is for interactive use only
- Fix some typos