TryFromWkt for integer geometries

[michaelkirk]

• [x] I agree to follow the project's code of conduct.
• [x] I added an entry to CHANGES.md if knowledge of this change could be valuable to users.

• [x] I ran cargo fmt

Fixes https://github.com/georust/wkt/issues/102

This is based on #101, which @rmanoka already approved (thanks!), but I'm going to wait just a bit longer to merge it in case someone else wanted to take a look at it. update: #101 has been merged, and this is ready for review!

[michaelkirk]

101 has been merged, and this is ready for review

[michaelkirk]

Rebased since merging #99

[michaelkirk]

bors r=urschrei

[bors[bot]]

Build succeeded:

• wkt