[chemfp] FPSFormat in OpenBabel

[Chris Morley]

In Openbabel's development code there is now an output format which 
writes OpenBabel fingerprints to an fps file.

I've taken the form in 
http://code.google.com/p/chem-fingerprints/wiki/ob2fps as the standard. 
The fingerprint strings seem to be required to have an even number of 
characters, otherwise FP4 with 307 bits would have 77 hex characters 
rather than the 78 it has on this page. This will not affect the 
fingerprint but might matter in how the reading and writing of fps files 
are implemented.

Chris