implement `binary` artifact
update a few cask to use `binary` artifact

This is obviously not an exhaustive list. I have included it in
the branch to demonstrate the new feature.
Updated linkinus information.
Merge pull request #2331 from karbassi/linkinus

Updated linkinus information.
Add cask for Hexels

No checksum for Hexels, it uses version 'latest'
Update transmission-remote-gui to v5.0.1
Merge pull request #2338 from tusbar/transgui-5.0.1

Update transmission-remote-gui to v5.0.1
Add cask for PixelStick
Merge pull request #2346 from tjwallace/pixelstick

Add cask for PixelStick
Merge pull request #2311 from goxberry/basictex-caveat

Add PATH caveats to BasicTeX cask.
Fix #2289

The link filename is not correct.
Merge pull request #2276 from stratoukos/2157-install-binary

Implement `binary` artifact
Merge pull request #2250 from lachlancooper/hexels

Add cask for Hexels
Merge pull request #2349 from linc01n/hotfix/2289

Fix #2289
Make links in README relative instead of absolute

Fixes #2347 based on recommendations in
https://help.github.com/articles/relative-links-in-readmes.