Underline current line: preserve highlighted matches

Changed vim actions for underline current line so highlighted matches are preserved.
Add minitest lang plugin
update submodules
Add reference to Visual mode

The modes section of the README file lacks a reference to visual mode, which is misleading. This fixes that.
Merge pull request #473 from jaredonline/master

Add reference to Visual mode in README
New mappings for the NERDTree:
 NERDTreeFind -> <leader>nf to find current file in the NERDTree
 NERDTreeToggle -> <leader>nn to access toggle functional fast
Updated Handlebars syntax
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