Use absolute links to docs

As atom.io displays the README on the [package page](https://atom.io/packages/vim-mode), links to the documentation are broken. The tag versus master thing sucks, but is probably better than a 404.
Adjust 'backspace' in command mode

In vim while in command mode 'backspace' will move the cursor left not delete characters.
"enter" key should move down one line in normal mode.
Add ctrl-[ keymapping to leave visual mode.

Sorry, missed this one yesterday.
visual mode default keybinding: delete with x
Merge pull request #52 from atom/use-absolute-links

Use absolute links to docs
Merge pull request #57 from Tarrant/master

Adjust 'backspace' in command mode
Merge pull request #65 from ctbarna/keymap-enter

"enter" key should move down one line in normal mode.
Merge pull request #68 from ctbarna/ctrl-bracket-extra

Add ctrl-[ keymapping to leave visual mode.
Don't style cursor in mini editors

Previously we accidentally styled the cursor in mini editors which
caused it not to appear in the settings view.

Fixes #67
Merge branch 'master' of github.com:atom/vim-mode
Update CHANGELOG.md
Prepare 0.7.1 release
Merge pull request #72 from zenhob/visual-mode-delete-with-x

visual mode default keybinding: delete with x
Clarify vision and development best practices