[SciPy-user] fisrt version of physical constants module + codata

[Gary Ruben]

Typo:

au = astronimical_unit

Useful sources for more units:
<http://en.wikipedia.org/wiki/Conversion_of_units>
<http://motionmountain.dse.nl/welcome.html>

I think you should establish a naming convention for us, imperial, 
(metric?) values. eg.
cup_us = 0.2365882365
cup = 0.25
This means changing gallon to gallon_us

Extra units I'd like to see:

length:
fermi = 1e-15

power:
dyne = 0.00001
erg = 0.0000001

binary prefixes:

kibi = 2**10
mebi = 2**20
gibi = 2**30
tebi = 2**40
pebi = 2**50
exbi = 2**60
zebi = 2**70
yobi = 2**80