Bug fix to address issue https://github.com/opencobra/cobrapy/issues/29 and to address a similar problem with the _genes attribute
Brought in bugfix.
Merge remote-tracking branch 'origin/master' into species
Updated convert to irreversible and revert from irreversible to deal with special case where a reaction had lower_bound < upper_bound < 0
corrected a typo bug
Added properties for genes and model to Reaction
created a parsimonious flux balance analysis script