An addition of a `vec_bsearch` function

I would like to add a method to perform a binary search on the vec.
My rationale is that currently there are no operations available on the vector in sorted form (withing diving into struct data), although it can be sorted. Instead of always performing a linear search, bsearch may be more appropriate. This also completes an encapsulation of the two algorithmic functions (qsort, bsearch) of C with the vec interface.