replace tslint with eslint for repo itself

I opened #305 ages back to move dtslint off tslint completely, as it has been deprecated for a very long time now.

however that turned out to be a huge task so im just trying to split it up a bit.

this PR moves the repo itself to being linted by eslint rather than tslint, but leaves the source roughly the same (using tslint).

some notes:

i turned off any rules your sources conflict with often (assuming they are just the chosen conventions for this repo)
there's a few switch fall throughs, on purpose it seems so i just ignored those
i turned off the recommended rule 'no-explicit-any' but maybe we should consider using unknown more etc or strongly typing those any uses

microsoft / dtslint