Major restructuring, untested

- Drop support for emacs 23 and below.
- Switch to setting "completing-read-function" (new variable in Emacs
  24) instead of defining advice on "completing-read".
- Rework old-style compatibility framework
- Version bump to 2.0
- Avoid spurious warning when ido-ubiquitous is enabled before ido during init
- Make ido-ubiquitous work in interactive forms of commands
Fix compile errors
Remove help text about interactive-mode problems.

This is fixed now, so the warning is no longer needed.
Add change log entries
Autoload fix
Update changelog
Doc changes
First working version after 2.0 refactor
Remove obsolete aliases
Add proper group declarations
Disable in "isearchp-read-unicode-char"

Fixes #9.