Fdint

- changed LICENSE to BSD-3-Clause
- improved README
- fixed test generation

- completely rewrote the package in Cython, which results in ~3x speedup over
gfortran + f2py, as well as more maintainable code
- added inverse Fermi-Dirac integral of order k=1/2
- added generalized Fermi-Dirac integrals and their first derivatives
- used in semiconductor physics and astrophysics
- added semiconductor-specific functions in the new `scfd` module

- fixed `python setup.py install` (was broken by build in-place)

- removed the python fall-back module (simplify maintenance)
- renamed `_fd` to `fd`
- fixed `from fdint.fd import fd1h`, etc. causing an error
- added vectorized forms of all functions, e.g. `vfd1h`

- fixed `pip fdint install` and `python setup.py install` failing if `numpy` is
not already installed