added test to check natural_abund
Merge remote-tracking branch 'upstream/staging' into staging
added orig sphinx ext
made some doc changes
Added a abundance_by_Z function to data.pyx
Merge remote-tracking branch 'upstream/staging' into staging
changed abundance_by_Z to module-level dict
fixed backgrounds
made abundance_by_Z interval open-open, added test to test for soundness of abundance values
Merge pull request #166 from scopatz/docfix

Docfix
updated abundance test
Merge branch 'abund' into staging
pep8 colpliance for njoy.py
njoy doc updates.
added experimental warning.
Merge pull request #167 from scopatz/njoy

Njoy Updates.