Kill jsts

[tcql]

This PR uses the greiner-hormann algorithm that I've been working on implementing. It's considerably faster than JSTS, and removes our dependency on JSTS, aside from turf-buffer.

There are likely some quirks / edge case failures here, but we'll deal with those as they come up. Here's some known differences in the behavior:

• Intersect / Union / Difference no longer will return linestrings or points for cases where polygons touch at only an edge or a point (or several edges or points)
• Returned point orders may be different

[jljorgenson18]

Was there a reason this was never merged?

[tcql]

@jljorgenson18 it was never entirely complete - the greiner-hormann module has been in a state of limbo for awhile. In the next few weeks we're doing some sprinting around polygon clipping algorithms, which means we'll hopefully have some news in terms of fixing turf intersect / difference / union soon.

[tcql]

Turfjs/turf-intersect#10 (comment)