Cut features back down to <0.4kb

Ignore the first 2 commits, they're from jayferd#21.

So there's minimalism, "do only a few things and do them well", yada yada, which I needn't repeat. But moreover, if there's features that we want to discourage people from using and that they also don't use, we should remove them.

I wasn't expecting you to roll out v5 so quickly, but I highly doubt anyone/hope no one is using the object literal shorthand, for the reasons listed in 751317e6c74d98c71abab52db7c200b7bf3d2c23, which is the only documented back-compat break in this PR, so I don't feel bad about rolling this out as a minor version (v5.1) if you don't.

I had a lot of fun watching the minified size go down, can you think of anything else to cut? If we cut `.extends`, `.constructor`, and `.Bare` we can get it down to 300 bytes, but I like all those.