Whitespace: tabs to spaces.
Change README TODO-list.
Fix imports.
Trailing whitespace.
Don't import constants as CONST
Python 3 compatability.
Remove '-' from negative near-zero in table. TESTS PASSING.
Merge branch 'feature/python3' into develop

Running under Python3.4
Provide mechanism for loading species by category.
Factory class for representing species.
Improve thermoinp.create_subset docstring
Encapsulate transformations in a new DB class

So far the class encapsulates

    database -> categories -> species strings

This was performed by _read_categories() and _read_species().
Add a constructor to SpeciesRecord (was Species)

Constructor now implements the body of _parse_species() (which now
invokes the constructor).
Add Species.formatted (original dataset string)
thermoinp.DB now transforms to SpeciesRecords
thermoinp.DB now has list_species, list_categories
Add an 'all' category to thermoinp.DB
Add a flag to SpeciesRecord indicating if product

This functionality is only present in thermoinp.DB
Implement additional categories in thermoinp.DB
Implement dict-like access to SpeciesRecords