The main objectif of this PR is to introduce a new module that abstracts Bootstrap component rendering (2d8ea6e).
Commit 63aab1e gives an example of how nitdoc will use these abstractions in the future PRs.
Also do some fixes and cleaning.
Pull-Request: #1174
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>