Use pkg-config for SDL build flags

This should be slightly more portable than before.
Add moire03.cpp

I had forgotten to track this before.
Change some int literals to floating-point

Apparently, pow(2, n) can be ambiguous in C++ (while pow(2.0, n) isn't).
Increase resolution for mandel_sine
Add new program sine_julia01

Currently, it just plots the Julia/Fatou set for the function
    z -> sin(z).
Add License (GPLv3)
Double resolution for mandel_ext_anim
Implement prototype of new coloring (sine_julia01)

The new coloring algorithm is based on the concept "external rays."  The
current prototype doesn't work too well, but it illustrates one possible
approach.