doc: remove legacy os_*.txt

keeping os_dos.txt, see #1115
doc: remove gui_w16.txt
doc: remove if_sniff.txt
doc: remove if_ole.txt
doc: remove workshop.txt
doc: remove netbeans.txt
doc: remove documentation for `:shell`

see #450
doc: cleanup

  * fix some links
  * typo
  * remove reference to hangul_input
  * remove unused vim2html.pl
doc: remove links to non existent files
Merge pull request #1268 from stefan991/cleanup-docs-2

Cleanup user documentation
Mark patches 363 and 366 NA.
vim-patch:7.4.375

Problem:    Test 63 fails when run with GUI-only Vim.
Solution:   Add guibg attributes. (suggested by Mike Soyka)

https://code.google.com/p/vim/source/detail?r=v7-4-375
Merge pull request #1254 from splinterofchaos/na-patches

Mark patches 363 and 366 NA; vim-patch:7.4.375
homebrew: use Makefile-defined defaults. #1259

Assuming homebrew always uses a clean workspace, a separate "cmake" step
is not necessary.