Add some extra possibly useful methods to vec.h

Mentioning @ssnyder and @amorley

Adds

• vselect : targeting similar functionality to _mm_blend x86-64 intrinsics
• vmin : targeting similar functionality to _mm_min x86-64 intrinsics
• vload : targeting similar functionality to _mm_load x86-64 intrinsics
• vstore : targeting similar functionality to _mm_store x86-64 intrinsics

vbroadcast which has similar functionality to _mm_set /_mm_broadcast intrinsics was in place already.

In the future depending on the usage we could consider adding SHUFFLE to get the functionality of _mm_shuffle if we want to use this for certain math operations that would profit. Although in this case how a fallback implementation would look like is less obvious.