Create an openblas-sys crate for OpenBLAS-specific APIs

[termoshtt]

As used in example code https://github.com/maoe/openblas-src/blob/print-config-fix/openblas-src/examples/config.rs to check OpenBLAS version for #60. This will be helpful in several context, and it worth including to openblas-src crate.

[IvanUkhov]

This calls for introducing openblas-sys, as it would be inappropriate to put this in any other -sys crates.

[termoshtt]

It makes sense. OpenBLAS has several special functions

• openblas_get_parallel
• openblas_get_num_procs
• openblas_set_num_threads
• openblas_get_num_threads
• openblas_get_config - openblas_get_corename

and these could be useful for tuning OpenBLAS behavior at the end user level.