Scjson support

PR ready. Merge with https://github.com/jbeard4/scxml-test-framework/pull/14

Currently 160 tests are passing, 55 from W3C.
Closing 12 issues: 8 errors, 4 fails.

Closes #189 
Closes #221
Closes #222
Closes #223
Closes #224
Closes #225
Closes #226 
Closes #227 
Closes #228 
Closes #230
Closes #272
Closes #284
It looks like you're supposed to do both: treat the expression as though it evaluates to false, AND raise error.execution.