v1.3-beta

Beta release of v1.3. This version does not run on Python 3.8 or 3.9, but still works with Python 3.6. All of the reconstruction code and special functions are now implemented in C. C99 features have been removed for portability, and only strict C89/C90 code is used (Also called ANSI C). A complex variables library has been added to make up for the lack of complex.h in C89, and no external libraries are used for librssringoccs (FFTW has been replaced with our own simple implementation of the Cooley-Tukey FFT algorithm). The library compiles with -std=C89, C99, and C11 on GCC and clang. Microsoft Windows compiler has not been tested.