Pyparallel can fail to compile

[ryanvarley]

We should add instructions to the readme on how to fix this. We should also address the warning.

python setup.py develop
Warning: Extension name 'pyparallel' does not match fully qualified name 'wayne.pyparallel' of 'pyparallel.pyx'
running build_ext
building 'pyparallel' extension
gcc -fno-strict-aliasing -I/Users/ryan/anaconda/envs/wayne/include -arch x86_64 -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -I/Users/ryan/anaconda/envs/wayne/lib/python2.7/site-packages/numpy/core/include -I/Users/ryan/anaconda/envs/wayne/include/python2.7 -c pyparallel.c -o build/temp.macosx-10.9-x86_64-2.7/pyparallel.o -fopenmp -lm -O3
clang: warning: -lm: 'linker' input unused [-Wunused-command-line-argument]
clang: error: unsupported option '-fopenmp'
error: command 'gcc' failed with exit status 1

[ryanvarley]

I fixed it by installing gcc with brew and then changing the GCC version with an env var

brew install gcc --without-multilib

CC=/usr/local/Cellar/gcc/7.1.0/bin/gcc-7 python setup.py develop

@atsiaras any comment on what you did?