Add :ToGithubBlame to open GitHub blame route

[synthead]

This should be a quick-n-easy one!

I often use this plugin to look up contributors to specific lines of code, and will sometimes look at PRs that shipped specific changes to do a little research on code decisions. When I use :ToGithub, I get a perma-link to the LOC, but it would also be really handy to also be able to do:

:ToGithubBlame

I propose that this ☝️ should be a new command offered by this plugin to go to the "blame" perma-link for the selected lines.

As we already know, :ToGithub builds a perma-link route that looks like this:

https://github.com/synthead/timex_datalink_client/blob/7dcbcfd35ffcfe559f67a23b6664e821edc9b612/lib/timex_datalink_client/protocol_3/start.rb#L10

The perma-link "blame" route is very similar, and looks like this:

https://github.com/synthead/timex_datalink_client/blame/7dcbcfd35ffcfe559f67a23b6664e821edc9b612/lib/timex_datalink_client/protocol_3/start.rb#L10

As you can see, instead of the "blob" segment, it simply uses "blame" instead.

Should be handy! I'd use it 😉