build failure on os x with g++ 7.2 and case preserving filesystem

[grumpyquant]

CVXcanon doesn't build from the pip package on OS X using g++ 7.2 (from homebrew) in the case where the filesystem is configured to be case preserving rather than case sensitive.

The problem is that the compiler confuses Eigen/Array for the array header in the STL, leading to errors:

  /usr/local/bin/gcc-7 -Wno-unused-result -Wsign-compare -Wunreachable-code -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -Isrc/ -Isrc/python/ -Iinclude/Eigen -I/usr/local/lib/python3.6/site-packages/numpy/core/include -I/usr/local/include -I/usr/local/opt/openssl/include -I/usr/local/opt/sqlite/include -I/usr/local/Cellar/python3/3.6.3/Frameworks/Python.framework/Versions/3.6/include/python3.6m -c src/CVXcanon.cpp -o build/temp.macosx-10.13-x86_64-3.6/src/CVXcanon.o
  cc1plus: warning: command line option '-Wstrict-prototypes' is valid for C/ObjC but not for C++
  In file included from /usr/local/Cellar/gcc/7.2.0/include/c++/7.2.0/tuple:39:0,
                   from /usr/local/Cellar/gcc/7.2.0/include/c++/7.2.0/functional:54,
                   from src/../include/Eigen/Core:153,
                   from src/../include/Eigen/SparseCore:4,
                   from src/../include/Eigen/Sparse:19,
                   from src/Utils.hpp:18,
                   from src/LinOp.hpp:22,
                   from src/CVXcanon.hpp:20,
                   from src/CVXcanon.cpp:16:
  include/Eigen/array:8:4: error: #error The Eigen/Array header does no longer exist in Eigen3. All that functionality has moved to Eigen/Core.
     #error The Eigen/Array header does no longer exist in Eigen3. All that functionality has moved to Eigen/Core.
      ^~~~~

It looks to me like the Eigen/Array header is not used at all in the project - if you remove this header then the build proceeds without error.

Can you please delete the Array header and repackage the library on pip?

[dmichalowicz]

I think this can be closed given #34, unless we want to wait for a pypi release first?