Merge pull request #57 from trontrytel/master

pull me
working mpdata-fct in 1d! (still only for positive-definite signal, and with assumed constant rho)
some more cleanups in test_mpdata_fct_1d
alloc() cleanups
introducing an mpdata_common.hpp file
quite a big commit introducing many cleanups in mpdata (mpdata_common and mpdata_fct_common); proper inheritance from mpdata_fct down till solver_common; draft of fct_2d
adding option-handling mechanism for mpdata + working sss option in 1d + test
adding sss option support in mpdata_2d
a draft of variable-sign code for fct_1d (still does not work correctly)
addint still apparently not functional toa option in 1d (+ new test)
adding eps option support + test; changing option handling from blitz::where() to std::enable_if - much faster!; adding a warning if compiling withouth fast-math
fix in mpdata_fct_1d for supporting transport of psi < 0