Periodictable

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New:

* mix_by_weight and mix_by_volume formula constructors
* use natural density to set density for isotope specific formulas
* add neutron_scattering function which returns xs, sld and penetration depth

Modified:

* need wavelength= or energy= for xray/neutron sld
* improved docs and testing

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New:

* support pickle: id(H) == id(loads(dumps(H)))
* support ions, with magnetic form factors and x-ray f0 scattering factor
* support py2exe wrappers
* allow density to be calculated from structure (bcc, fcc, hcp, cubic, diamond)
* estimate molecular volume
* support private tables with some values replaced by application

Modified:

* rename package periodictable
* rename table to periodictable.elements
* neutron sld returns real and imaginary coherent and incoherent
instead of coherent, absorption and incoherent
* bug fix: sld for H[2] was wrong when queried before sld for H.
* remove CrysFML ionic radius definitions

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Modified:

* Restructure package, separating tests into different directory
* When defining table extensions, you should now do::

from elements.core import periodic_table, Element, Isotope

rather than::

from elements import periodic_table
from elements.elements import Element, Isotope