Merge pull request #47 from cyisfor/master

Stacking in any direction
Documentation for `//stack2`, code style fixes, add author section to README.
Update `stack2` API documentation.
Oops, fix `//set`.
Slight optimization to //set

Just noticed I box the one type version in a list, to avoid testing
whether it's the one type version, but have to test for that to decide
whether to box it or not. Should shave like a whole 3ms from each //set
command.