Adds jumping to previous and next changes.

- Adds two new commands: "git_gutter_next_change" and "git_gutter_previous_change"
Adds default windows keymap.

- ctrl+alt+j is already used for the Pretty JSON plugin.
- uses ctrl+shift+alt+j and ctrl+shift+alt+k to align with vim up and down.
Updates readme for keymap info.

- Adds sentence in beginning.
- Adds default bindings.
Refactors.

- Region names as keys mapped to icon names.
Retina Icons
Cleanup.

- Removes need for except StopIteration.
Removed placeholder
fixing not loading live mode on startup in ST3, this is done by way of hack which defaults setting of live mode to True when the reading of config file fails.
Make changes to @DavidLGoldberg's pull request

Put the change command into its own file, dry it up
Add default OSX keymap
Make lines over 80 chars PEP-8 comply
Make lines jumps only jump to blocks over changes

Instead of every line in a block of modifications which is tedious
Make jumping between changes loop back around
Merge branch 'master' of github.com:unphased/GitGutter into unphased
Update README.md

- Updated key bindings values as changed from "previous" to "prev"
- Mentioned that there are default Mac bindings as well.
Fix #59 by redirecting stderr.
Change README...

I think it makes more sense to have a section about the actual feature than the keybindings and how to change them. Changing default keybindings isn't a GitGutter feature but *Sublime* feature, so anyone who would like to change them can easily figure out how with a little googling. Plus I don't want to put too much README real estate devoted to this feature since it is not core GitGutter functionality. I would like to get some default linux key bindings tho.
Make keys easier to read
Merge branch 'master' of github.com:tuvistavie/GitGutter into tuvis
Add non blocking mode to run gitgutter in seperate thread
Add non_blocking to README settings
README change

This feature has its own section below