Use np.fromfile to drop struct import.
Add support for little-endian CSS files.

Test files were produced using the 'endi' program from MINEOS on the
existing big-endian file.
Untested support for CSS files in ASCII.

These data encodings are defined on page 33 of the CSS reference schema,
but it's not clear if there are any separators between each value. I
also do not have any samples files, so this bit remains untested. Maybe
someone will provide an example some time.

The reference schema can be found in the Pisces repository:
https://github.com/jkmacc-LANL/pisces/tree/dev/docs/data
Fix CSS on Python2.
ChangeLog CSS additions.
Merge pull request #881 from QuLogic/css-dtype-additions

CSS dtype additions