Upgrade extension to new GitHub changes

• Update due to GitHub's DOM changes #96

Mark viewed files

• Add checkmark next to viewed files #91 (thanks @sunnymis)

Firefox Support

• Added initial Firefox support #88 (thanks @candentira)

Add "Viewed files" support

• Add "Viewed files" support #83 (thanks @candentira and @aklotos)
• Remove sticky header code as it is already implemented by GitHub #79

Fixes and improvements

• Show the new name/location of files that have been renamed #75 (thanks @cluhm)
• Improvements to GitHub Enterprise Support #73 (thanks @fregante)

Full width improvement

• Save full-width configuration #63 (thanks @Notaphish)
• Fix regression affecting dark mode

Dark mode improvements

• Improvements to Dark mode #62 (thanks to @Notaphish)

Dark mode

Added Dark mode #59

UI Improvements

UI Improvements:

• Change styling of search box
• New icons for close button, comment indication and settings icon
• Add highlight to files while searching
• Add link to settings page
• Stick search and buttons to the top

Diff stats and options page

• Added options page
• Added Diff Stats next to each file #49 (thanks @evansiroky)