ctags: add

Ctags generates an index (or tag) file of language objects found in
source files that allows these items to be quickly and easily located by
a text editor or other utility. A tag signifies a language object for
which an index entry is available (or, alternatively, the index entry
created for that object).

Signed-off-by: Igor Santos <igor.santos@aker.com.br>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>