highlighter: get rid of s:Get() function
highlighter: get rid of s:Get() function

Replace by a function that retuns the to be executed highlighting string

Should in theory be a bit faster, since the same function does not have
to be called 5 times per highlighting group.

It probably is not much better, but here are some random numbers:

Profiling:

Previously:
count  total (s)   self (s)
  199   0.022973   0.009909     let cmd = printf('hi %s %s %s %s %s %s %s %s', a:group, s:Get(colors, 0, 'guifg=')…

New:
count  total (s)   self (s)
   79   0.010166   0.000862     let cmd = printf('hi %s%s', a:group, s:GetHiCmd(colors))

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