Added more documentation, removed warning about HALIDE_PATH unset, added explicit errors when build steps fail.
Added more documentation, removed warning about HALIDE_PATH unset, added explicit errors when build steps fail.


Former-commit-id: f1011af2c73546ab966b680e88578addf1263e01
Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide