* Add WHO standards for head-circumference-for-age
* Add WHO standards for body-mass-index-for-age
* Add additional WHO standards for ages 0-13 weeks for wfa, lhfa, hfcfa, and bmifa
* Extract tests into proper tests.py, runnable by nose
* Major refactor of pygrowup module
* Change import behavior, class names, and usage
* Better error checking, sensible exceptions, and improved exception handling
* Intelligently switch indicator tables when appropriate (e.g., change table lookup from whl to wfh if child is too tall for wfl)
* Reformat tables when loading into memory for faster lookup performance
* Use python's logging instead of print statements
* Various bug fixes