Added some minor features

Hi! First of, beautiful work that you have done.
I've been using your plugin for a while, and it's time I thought I make some contributions to make it better,

I have implemented very basic ones, but I intend to add more in future.
Here's what I've done so far
- Implemented the change region to Upper Case [ M - U ]
- Implemented the change region to Lower Case [ M - I ]
- Added Redo [ C-X C-/]

Also I noticed there's no 'select all command', I tried adding [C-X H] but it doesn't work, so for the time being i used [C-X C-A]

Let me know if you need any further modifications on these.

Cheers,
Udit