Border textures

[head-gardener]

#97 Allows for more interesting border designs by drawing textures above them. Basically a sway-borders adaptation.

Currently requires corner_radius 0 and border pixel|normal >0 to be set in config.

Command syntax: border_texture [bevel|*file path*].

[head-gardener]

Some moments I haven't figured out:

• Rounded corners are still WIP.
• Current approach to scaling textures might be overly complex and performance profiling is required to figure out whether this complexity is worth it.

[AnotherRandomGitHubAccount]

Is this branch dead?

[head-gardener]

@AnotherRandomGitHubAccount Probably, haven't looked into master in a while.