Unfunction ruby-electric-is-last-command-char-expandable-punct-p.

It is only used once and the name is so long it doesn't pay.
Suffix ruby-electric-expandable-bar with -re.
Allow ruby-electric-mode to be disabled by introducing a dedicated key map.

Electric key bindings are now defined in ruby-electric-mode-map instead
of overwriting ruby-mode-map.
Add ruby-electric-mode-hook.
Improve ruby-electric-bar like others.

- Use looking-back.
- Set this-command to self-insert-command if not electrified.
Define a master constant ruby-electric-delimiters-alist.

From which the initial values of the following variables are generated:
- ruby-electric-matching-delimeter-alist
- ruby-electric-mode-map
- ruby-electric-expand-delimiters-list
Use a remap in binding ruby-electric-delete-backward-char.
The check with ruby-electric-cua-delete-region-maybe is now obsolete.
Totally revamp electric keywords and then introduce electric return.

Properly detect modifier keywords making use of ruby-mode's indentation
level calculator.

Now block-mid keywords (then, else, elsif, when, rescue and ensure)
become also electric with automatic reindentation.

Disable smartparens-mode's end keyword completion, since ruby-electric
has become more clever at it.

The custom variable `ruby-electric-keywords` is changed to
`ruby-electric-keywords-alist`, allowing user to fine-grained
configuration.
Mark destructive commands as so.
Add standarized comments for ELPA integration.
Bump version to 2.0.