SpecMiCP_cython handles c++ errors

Fixes issue #31. The C++ errors are transformed into python errors
according : http://docs.cython.org/src/userguide/wrapping_CPlusPlus.html#exceptions
Note : this is a manual process and the function that may raise an
exception must be identified and flag with 'except +'.
The most obvious one were identified and flagged in the following modules :

• constraints
• database
• solver