This is a follow up to 545afc15.

Tested on a brand new app to exactly match current byebug's behaviour.

[ci skip]

* Indent after private/protected
* Ruby >= 1.9 syntax for hashes
* Prefer method { do_stuff } instead of method{do_stuff} for single-line blocks.

[ci skip]

* it's Action Mailer not ActionMailer
* it's Action Pack not ActionPack
* it's Active Support not ActiveSupport

/cc @fxn

see: https://github.com/blog/738-sidejack-prevention-phase-2-ssl-everywhere

We have three or four different introduction sentences to the guides.
After this commit, we use the same one everywhere.

Talked with @fxn about this. Bullet points should have periods at the ends.

This reverts commit f5b9ed4f.

REASON: Translation work can not be done in the docrails repository

- remove query_stats plugin reference in debugging guide since it is no longer maintained.
- remove exception_logger plugin reference in debugging guide since it is no longer maintained.
- update query_reviewer url to the latest one on github.

In Textile `*` would convert to `<strong>`, but in Markdown we have to
use `**` instead.