blas install docs, other install polish
trivial makefile grooming
auto-configure linux/osx build differences

- set cxx as needed (clang++ on os x)
- set stdlib flag for os x 10.9 (CUDA libc++ workaround)
- link ATLAS properly for non-MKL installation whether linux or os x
Merge pull request #305 from shelhamer/install-doc-blas-platform

Document BLAS install, tailor Makefile and Makefile.config to platform