Remove magic numbers

[ccarouge]

Magic numbers:
es=6.1094*np.exp((17.625*(ta-273.15))/(ta-30.11))
es=6.1094*np.exp((17.625*(ta))/(ta+243.04))
rh=((hus*(plev-es))/(0.622*(1-hus)*es))
t_dewpoint=((243.5*np.log(e/6.112))/(17.67-np.log(e/6.112)))+273.15
adiabatic_adj=850*(ta-cur_t)*(.00066)*(1+.00115*cur_t)
180: conversion between rad and degrees
erad = 6371e3 : Need to say what it is.
re=6371e3: Same magic number as erad above but with a different variable name and re-defined in a different function

[aidanheerdegen]

Or replace with metpy. See #1

[greensh16]

Has now been replaced with metpy.