Initial FileReader bindings

[nwolverson]

Not sure if this belongs in here or a separate lib. Either way I'd put some Aff layer on top separately.

Unfinished are error - is DOMError used somwhere? - and result - which I think can be null | string | ArrayBuffer

[garyb]

I'll take it, thanks!

I don't remember encountering a DOMError type anywhere else in the stuff I've worked on, or if so it's been ignored/unimplemented also.