Note: there are three changes to ascii_isident. Reverting first two (in
find_special_key and first in get_special_key_code) normally fails the new test
with empty &isident, but reverting the third does not. Hence adding `>` to
&isident.
Ref vim/vim#2389.
Regarding the individual items in the header:
`Vim - Vi improved by Bram Moolenar`
Bram Moolenar is already mentioned throughout the documentation, as
well as the intro screen.
`:help uganda`
It's already shown to all users who don't use `shortmess+=I` upon
starting nvim, and is already placed prominently in help.txt, i.e.,
`:help` run with no arguments.
`:help credits`
Already mentioned near the top of help.txt.
`README.md`
Already mentioned in develop.txt.
Move files from src/ to src/nvim/.
- src/nvim/ becomes the new root dir for nvim executable sources.
- src/libnvim/ is planned to become root dir of the neovim library.
