Ignore distutils directories.
.gitignore: small simplification.
Forward **kwargs to FAUST to ffi.verify().

Forward **kwargs that are passed to FAUST on to ffi.verify().  This makes it
possible to add additional libraries to link to and to extend the compiler
flags.

This commit also adds "-march=native" and "-O3" to default compiler flags, the
reasons being:

- compilation happens at run time, so -march=native should be safe,
- FAUST programs usually profit from -O3, especially since it activates
  auto-vectorisation, and
- since additional flags are appended to this default, you can override them
  anyway in situations where they *are* bad.
Add -c/--cflags option to __main__.

Add -c/--cflags option to __main__, so you can override the CFLAGS of the demo
application.
Make a minor change to the doc strings.
Extend README a bit.