implement engineering verification; no actual tests yet, of course (fixes #206)
failures should override successes, obviously
look up the code from the jurisdiction, unless override_code is specified
implement a test for NEC 2014 690.7(A) (fixes #219)
add methods for iterating over component nodes
display temperatures as fahrenheit in error messages
implement test for NEC 2014 690.43 (fixes #217)
implement a test for NEC 2014 690.9 (fixes #222)
implement a test for NEC 2014 690.12 (fixes #223)
implement a test for NEC 2014 690.13(D) (fixes #224)
exclude wires from test for 690.43 (for #217)
record dependency on the units module
implement tests for NEC 2014 690.6 (fixes #218)
implement a test for NEC 2014 690.13 (fixes #225)
fix a small mistake
fix terminology
wires count as intervening components (for #225)
implement a test for NEC 2014 690.15(D) (fixes #226)
NEC 2014 690.13(D) only applies to dc (for #224)
fix iterator length