[wip] buffer clipboard support

[Consolatis]

This PR allows to copy text from the buffer by selecting it with the mouse.

This is my first time working with go so it might be possible I did something stupid because I don't know the language or its default patterns. Feel free to point out any such issues.

Missing:

• Verify custom pane_width settings for nicknames and text
• Maybe abstract setting the clipboard via OSC 52 (including base64 encoding) to make it easier to switch to tcell (once supported)
• Update docs
• Clean up some comments
• Revert i -> j change
• May need to consider unicode char width != 1 when translating from cursor coordinates to runes
• Use terminfo Ms arg to work on different terminals + feature detection

^ Example:

test -n "$(tput Ms)" && tput Ms c "$(printf "%s" "enjoy your new clipboard content" | base64 --wrap=0)"

When testing via tmux: set -w set-clipboard on.

[delthas]

Oh, I never saw this PR because it was made against your own master branch

[Consolatis]

Oh, I never saw this PR because it was made against your own master branch

That was intentional as can be seen in the screenshot above: I prefer not to expose my private email address to the mailing list and am not aware of any other official public git repo that I could post a PR / MR against.

Thus this hack to generate https://github.com/Consolatis/senpai/pull/1.patch which I posted into the IRC channel at that time. Same for the other 2 PRs against this repo.