Extern_c, power, hypot, checkerboard (expr and Halide::select)
Extern_c, power, hypot, checkerboard (expr and Halide::select)

- extern_c example
- power function image generator using extern_c
- power function image generator using Halide::hypot
- native Halide checkerboard generator
- colored checkerboard generator using nested Halide::select

cod3monk3y/halide,cod3monk3y/halide,cod3monk3y/halide,cod3monk3y/halide