MAINT: dotblas: factor out all gemm and gemv calls
ENH: improve add_newdocs performance

replace slow exec with a direct __import__.
improves `import numpy` speed by about 10%.
Merge pull request #3980 from larsmans/refactor-gemm-gemv

MAINT: dotblas: factor out all gemm and gemv calls
Merge pull request #4064 from juliantaylor/import-speed

ENH: improve add_newdocs performance