Starting to document the changes around password hashers
Adding a section for migrating old passwords
Removing references to BlowfishPasswordHasher
Add password hasher changes to the migration guide
Copying changes to the actual english file
Fixing some namspaces and copying to the sr language
Correcting namespace
Adding not about the new namespace created for Auth things
Fix typo.
Use bcrpyt instead of blowfish

bcrypt is a much more common name for blowfish.
Fix formatting and remove un-important methods.

Not every method needs a callout in the book. These methods are not as
important and can exist only in the API docs.
Updaing password migration example
Removing serbian file that is not currently translated
Fixing table name in auht docs
Merge pull request #1401 from cakephp/3.0-password-hashers

3.0 password hashers