CIF parser raises YappsSyntaxError instead of StructureFormatError for malformed files

[kwagoner94]

Problem

Malformed CIF files now raise YappsSyntaxError from the underlying PyCifRW parser. This breaks tests that expect StructureFormatError.

Proposed solution

Catch YappsSyntaxError and raise StructureFormatError instead in the CIF parser.

[sbillinge]

Can we just handle YappsSyntaxError instead of StructureFormatError rather than catch and raise? Just a thought.

To decide, can we spend 5 minutes understanding the difference and which is a more appropriate exception? Then we can just decide and go with that.