Zencoding-vim to have a ftplugin directory.

Zencoding used to map its mappings in all filetypes which was causing
strange behaviours. Now it is limited to html filetype to cage it in
only that type.
Integrated ag, the_silver_searcher plugin.

Deleted -H unknown parameter.
Added ag, the_silver_searcher executable configuration line, as well as

some Aliases and some reorderings in the file.