Underline current line: preserve highlighted matches

Changed vim actions for underline current line so highlighted matches are preserved.
Add minitest lang plugin
New mappings for the NERDTree:
 NERDTreeFind -> <leader>nf to find current file in the NERDTree
 NERDTreeToggle -> <leader>nn to access toggle functional fast
Update git language submodule

Updates the git language submodule to include a fix for syntax
highlighting of git commit messages. There is only one new commit
introduced by updating this submodule.

https://github.com/tpope/vim-git/commit/4bc24f694d12bea02f8a97a02efc2987a5cb66f9

https://github.com/tpope/vim-git/compare/75bc1628833ee1f1d8ecb8a66c5df852554c9a19...4bc24f694d12bea02f8a97a02efc2987a5cb66f9
Move scary old upgrade notes to bottom of readme
Link to upgrade notes section
Ctrl-P inserts path only after space
Remove superfluous map to :CtrlP
Remove %% cmap
Don't blow up if ~/.vim/_* is missing
Merge pull request #487 from tpope/safe_dir_settings

Don't blow up of ~/.vim/_* is missing
Merge pull request #486 from tpope/hanging_percent

Remove %% cmap
Merge pull request #483 from tpope/discretionary_ctrl_p

Limit Ctrl-P cmap to only operate after space
Merge pull request #478 from moutten/update_git_language_submodule

Update git language submodule
Merge pull request #476 from a-b/master

New mappings for the NERDTree
Merge pull request #468 from robertomiranda/add_minitest_lang_plugin

Add Minitest lang plugin
Merge pull request #485 from tpope/superfluous_ctrlp_map

Remove superfluous map to :CtrlP
Merge pull request #482 from galtenberg/master

Move scary outdated upgrade instructions to bottom of README
Fix the URL introduced by #482
Merge pull request #459 from robi-wan/patch-1

Underline current line: preserve highlighted matches