v0.8.1: Bug fixes on 0.8.0.

Changes:

• Fix github remote parsing bug with webdiff #292-style invocation
• Using react-router to include the file number in the URL (e.g. /2) for easier refreshing.
• grid pattern to indicate transparent regions of images
• Fixed bug where unchanged regions would oscillate with "onion skin" mode
• "Blink" image diff mode now auto-blinks every 0.5s
• A banner now advertises when there are no changes between the two files.
• Support for GitHub auth via a .githubrc file (same as gcli)