#235 CtagsInterface: Per-project Ctags invocation options

Currently the Ctags invocation options in CtagsInterface are global and used for all tagging tasks. It is useful to be able to configure project-specific Ctags invocation settings. For example, a large C project (e.g. Linux kernel) can contain many html / perl / other files which I may not be interested in, so I may want to specify "--languages=c" to Ctags. Another project may be a perl project, in which I am interested in "--languages=perl".
Moreoever, the auto-update of CtagsInterface doesn't allow me to change the "--languages" option just once to tag a project, and then restore the previous setting, as the first save of a file will rerun Ctags with the restored setting, and the file may be removed from the tag database.