Reduce allocations in per-request methods to improve performance

[smarterclayton]

As part of performance evaluations in Kubernetes go-restful was a
significant source of time and more importantly memory allocations
during request processing. Profiling uncovered a number of places
where some specific changes could be made to avoid allocating which
reduces CPU use during garbage collection on per-request actions.

The following three changes were the smallest / easiest and should
be relatively easy to review. There are other hot spots that still
need to be investigated which may require more aggressive changes.

Reduce allocations in route selection

The use of new arrays for each phase of detectRoute can be simplified: each
pass filters the existing array and whatever is left at the end is
returned. While somewhat harder to read, this method is a significant
source of allocations.

Reduce allocations in Accept and Content-Type matching

The mime handling methods can do a single pass over the header without
needing to allocate. This improves performance of these methods in higher
traffic API servers.

Prevent additional allocations when sorting routes for selection

Use of an uninitialized array and the use of sort.Reverse cause extra
allocations in request routing which are unnecessary.

[smarterclayton]

@wojtek-t FYI

[emicklei]

@smarterclayton thank you for your effort and work to improve the performance.

To be honest, I did not spent time on measurements to see where it can be improved.

I will review your changes carefully.