TODO - Quantum-ClebschGordan

(in no particular order)

* efficiency -- cache __check_state in a __state attribute
* efficiency -- cache calc calls
* memoize __seq calls
* add methods like  all_js, all_j2s, all_ms, etc ..
* more thorough tests
 - full coverage on __check_state
 - test explode()
* a /bin script for explode (takes j1, j2)
* review POD
* review comments; move appropriate info to POD
* efficiency -- try to reduce use of Number::Fraction objects? or look at speeding up Number::Fraction internals??