More bindings for split panes

* added more Vim bindings to focus and close panes
split.md: fix key order so the docs line up nicely
rename splits.md -> windows.md to more closely reference the Vim docs

There are more than just "split" commands in this document now, and
in the Vim docs, all of the `ctrl-w` commands are in `windows.txt`
add missing close binding: ctrl-w ctrl-q
add additional ctrl-key bindings for pane movement
Don't throw errors on invalid regexes
Merge pull request #164 from atom/fix-search-error

Don't throw errors on invalid regexes when searching
:lipstick:
Add changelog entry for search fix
CHANGELOG: added bindings for split pane movement
Merge pull request #162 from atom/more-split-window-bindings

More bindings for split panes
CHANGELOG: fix search with an invalid regex

Conflicts:
	CHANGELOG.md
README: remove completed TODO features, fix doc link
README: remove completed visual modes from TODO
Merge pull request #171 from zenhob/doc-fixes

README: fix TODO and doc link