wordcount: only test against complete filetypes
wordcount: only test against complete filetypes

Put a word-boundary regex atom before and after the current filetype, to
make sure that a `C` filetype won't be detected as a filetype that
enables the wordcount extension. (`c` matches asciidoc).

chrisbra/vim-airline,bling/vim-airline,rchicoli/vim-airline,yzhou61/vim-airline