[lib] Fix version number check

Add function that correctly compares two version numbers, and returns
`=`, `<` or `>`, according to the case.

e.g.:

 * `10.9`     `10.9.0`  =>  `=`
 * `2.1.10.1` `2.2`     =>  `<`
 * `3.2.09`   `3.2.10`  =>  `>`
Add MIT license
[lib] Add `gitconfig` to the FILES_TO_SYMLINK list

This change is made because I:

 * rarely use private git configurations
 * usually stored the git credentials in `~/.bash.local`