As magit is required, this seems good practice to declare the dependency
first
Explicit from where the TAGS generation comes from.
Extract the used binary (ctags-exuberant) to generate the TAGS file.
Open the means to override the default configuration (on my machine,
ctags is not ctags-exuberant)
Not sure this file really needs to be `gitted`
Merge pull request #1 from ardumont/master

Make ctags binary & message prefix configurable. Remove errant ctags-file.