replace tslint with eslint for repo itself

[43081j]

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

[sandersn]

Seems like a good start. I'll merge shortly.

[43081j]

Great, thanks a lot for taking time to pick it up and get it merged 👍