fix tsc types

[paulirish]

Back in #69 @brendankenny added some typechecking stuff

but it looks like its atrophied and there are now 25 errors.

it was never part of the test script or any ci stuff. shrug.

[brendankenny]

Some of this is typical easy tsc updating stuff, some of it is better checking of over-cleverness in the output that should probably have its implementation simplified (but may be a breaking change) and some of it is just older-style javascript that's difficult to type (e.g. object properties where it's hard to prove to the compiler that they won't be null by the time they're accessed).

Definitely doable, but it'll take some real code changes, not just types, so I'm giving up for now since it isn't a 10 minute job :) Anyone should feel free to take a stab at it.