some renamings

It’s almost 1am, so I’m only scratching the surface, mechanistically
applying the renames that I’ve written down in my notebook:
  * typeSignature => info
  * declarations => decls
  * nme/tpnme => termNames/typeNames
  * paramss => paramLists
  * allOverriddenSymbols => overrides

Some explanation is in order so that I don’t get crucified :)

1) No information loss happens when abbreviating `typeSignature` and `declarations`.
We already have contractions in a number of our public APIs (e.g. `typeParams`),
and I think it’s fine to shorten words as long as people can understand
the shortened versions without a background in scalac.

2) I agree with Simon that `nme` and `tpnme` are cryptic. I think it would
be thoughtful of us to provide newcomers with better names. To offset
the increase in mouthfulness, I’ve moved `MethodSymbol.isConstructor`
to `Symbol.isConstructor`, which covers the most popular use case for nme’s.

3) I also agree that putting `paramss` is a lot to ask of our users.
The double-“s” convention is very neat, but let’s admit that it’s just
weird for the newcomers. I think `paramLists` is a good compromise here.

4) `allOverriddenSymbols` is my personal complaint. I think it’s a mouthful
and a shorter name would be a much better fit for the public API.