ctags: execute ctags depending on filetypes

[ludovic-gonthier]

Extends the current map <leader>rt to execute the correct ctags options depending on the filetype.
Base the options on different ctags configuration files suffixed with the filtetype

[ludovic-gonthier]

Or maybe try to use https://github.com/vim-php/phpctags to see if the output tag fits better to PHP use (more logical class found)