Minor buffer.c style cleanups
Remove unused arg 'defer' in 'job_start' #1000

* With the changes in commit
  "events: Refactor how event deferral is handled"
  (2e4ea29d2c7b62eb8baf1c41cd43433e085dda0) the function argument
  'defer' of 'job_start' and member variable 'defer' of 'struct job'
  can be removed.
* Update/Fix the documentation for function 'job_start'.
Remove FEAT_MOUSE_JSB

This is never built and references some obscure jsb terminal
Merge pull request #934 from fornwall/remove-FEAT_MOUSE_JSB

Remove FEAT_MOUSE_JSB
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>