added install command

autoload/vs/cmd.vim

function! vs#cmd#Build(bang,...)
    echon "vim-vs: " | echohl Identifier | echon "building..." | echohl None
    silent! exe 'make!'
    silent! exe 'make! '. a:bang
    redraw!
    if !a:bang
        cwindow

ftplugin/vs/commands.vim

let g:vs_loaded_commands = 1
nnoremap <silent> <Plug>(vs-build) :<C-u>call vs#cmd#Build('')<CR>
nnoremap <silent> <Plug>(vs-install) :<C-u>call vs#cmd#Build('install')<CR>
nnoremap <silent> <Plug>(vs-doc) :<C-u>call vs#doc#OpenBrowser()<CR>