Remove obsolete test/__main__.py.
Split up tests into one per class.

Split the tests up into one per class, that is, one for FAUST, and one each for
Python{UI,DSP}.
Remove need of "faust_float" argument to PythonDSP.

Remove the need of the "faust_float" argument to PythonDSP by getting its value
through the cffi.ffi object passed to it instead (via ffi.getctype()).  This
avoids the potential for passing a different value of FAUSTFLOAT than what was
set during compilation of the FAUST DSP.
Tests: don't return faust_float from init_ffi().

Don't return faust_float from init_ffi() since it isn't used anywhere.
Document the dsp_class argument.
PythonDSP: change argument order, adapt doc string.

Change the argument order so that faust_flags is third, followed by the various
class constructors.  Adapt the documentation to match.
PythonDSP: raise ValueError when fs <= 0.
Convert fs to int before passing to initmydsp().
Pass the FAUSTFLOAT value and DSP file to init_ffi.
Tests: test for dsp.dsp attribute.
Tests: greatly expand PythonDSP tests.
PythonMeta: always create a .metadata attribute.
Add a simple test suite for PythonMeta.
FAUST: add info on LDSHARED environment variable.

It turns out that to fully compile with a different C compiler, you also need to
override the LDSHARED environment variable. However, the required options
"-pthreads -shared" are not automatically set, so you have to set those, too.