Code Cleanup

[ctcyang]

Some TODOs:

• make include order follow Google C++ style guide
• make code follow clang-tidy
• get rid of #define private public, either by making all classes structs or adding accessors
• move unit tests to within each folder and of naming spgemm_test.cu
• add Makefile support for unit tests
• get rid of env vars, by making global static context object
• make CSR only vs. CSRCSC matrix granularity rather than global granularity
• change std::cout's to use GLOG or some other type of logging library
• get rid of Boost dependecies on program_options and test with commandline flag library such as gflags and googletest