Swap out json for ujson

[pmlandwehr]

ujson is a faster version of json written in C. Back in the day, it beat both simplejson and json pretty significantly in some tests. On the other hand, it cares more about speed than error checking.

[martinburch]

Hi, and thanks for taking the time to set up this PR. I wasn't aware of ujson but it definitely looks worth a closer look for other projects. However, it's not right for this project.

• The big delay with getAPIPage() is not decoding JSON, but waiting for state.gov to respond.
• We don't want to hit state.gov too fast, so any minor delays introduced by slow, sequential JSON processing seem acceptable.
• I am concerned about ujson's error handling. We don't want any broken page responses (e.g. 404s or 500s) silently misinterpreted as valid JSON. The code should fail loudly instead.

So, I won't be accepting this PR. I'll leave it open for a little while, though, so others can see it. Again, thanks for making an effort. So many commits!