Minor buffer.c style cleanups
Merge pull request #998 from war1025/dev/buffer_cleanup

Minor buffer.c style cleanups
eval: re-remove USE_CR #1002

It was already removed in 01ca460 and I erroneously introduced it again in
PR #978.
Units: Move NULL, OK, and FAIL to helpers.moon. #982
eval: re-add has('mac') and has('macunix') #976

They were removed but they can be handy to separate some things to do at
startup in a .vimrc for example.
doc: Remove 'textmode'

by @mhinz
runtime: Remove 'textauto'
doc: Remove "h" flag of 'highlight' option

HLF_H is an obsolete flag and got replaced by HLF_E.

From: Marco Hinz <mh.codebro@gmail.com>
Change vimdir path from vim to neovim
Add install target for runtime dir
Merge pull request #1005 '[RFC] Change vimdir path from vim to nvim'