COFFEE supports dense linear algebra libraries

COFFEE can now transform left-hand side kernels into sequences of calls to linear algebra libraries' DGEMM. So far, MKL, ATLAS and EIGEN are supported, and the code can be easily extended to other libraries.

This depends on a Pull Request 46 in mapdes/ffc
I'll rather clarify the method's __doc__. It actually changes the storage layout of arrays: *from bi-dimensional arrays to one-dimensional arrays* (i.e. it flattens arrays whose size is known at compile time, e.g. our basis functions, because that's the storage layout imposed by BLAS).