Enhancement: add h/H key in diff view

[randy3k]

close #669

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• 2017-07-18T03:18:38.743Z:7930bd0: The pull request was created
• 2017-07-18T03:19:39.320Z:7930bd0: @randy3k checked I have read and agree to the [contribution guidelines](https://github.com/divmain/GitSavvy/blob/master/CONTRIBUTING.md)..
• 2017-07-18T03:19:39.877Z:7930bd0: @randy3k checked All related documentation has been updated to reflect the changes made. _(required)_.
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• 2017-07-18T03:19:56.192Z:7930bd0: @randy3k selected patch as the semantic version.

[divmain]

Could you rebase this to get rid of the master merge commit?