Add `todo' alias (.bash_aliases)

I try to use comments with todo notes frequently. This alias helps me,
finding all those comments in the current working directory and all of
its subdirectories.
Update `todo' alias (.bash_aliases)

It is not a really good idea, to search for all `###' in a directory
containing many files with Markdown syntax ...
Small cleaning updates to .vimrc
Update git configuration and bash aliases

* Don't use tabs on gvim
* Use meld as diff tool