Basic blas_int, lapack_int definition and CBLAS enums

This crate serves as the very elementary definitions for all BLAS distributions (controlled by cargo feature ilp64):

• blas_int for BLAS integers (used for dimensions)
• lapack_int for LAPACK integers (used for dimensions, flags and integer scratchs iwork)

This crate also defines CBLAS enums.

Cargo feature

• ilp64: control number of bits of blas_int and lapack_int.
• lp64_as_int: use core::ffi::c_int instead of i32 as integer of LP64 scheme.

Both cargo features are not enabled by default.