Adding link to eigen directories

[kmader]

adding link to eigen3 path to hopefully address this issue

[milhidaka]

Thank you for the pull request.
I would like to ask two updates.
First, allow users to override include path because eigen is not necessarily in /usr/include/eigen3.
In brew, it is installed in /usr/local/include/eigen3.
So, please add override option like:

generate(graph, include_path=["/usr/local/include/eigen3","/some/other/path"])
=> args.append("-I/usr/local/include/eigen3"), args.append("-I/some/other/path")

If there is include_path item in kwargs, it should be used. If it is not, default (/usr/include/eigen3) should be used.

Second, your patch only applies to _compile_fallback_asmjs, but should also applies to _compile.