Beta-4.1

Welcome to Vektor Beta-4.1!

This release includes some fairly niche but useful capabilities: you can now provide a function to be run before VK's router called an 'inspector', which allows code that can view a request without interacting with or modifying it in any way.

It also includes a SwapRouter method which allows wholesale swapping VK's router at runtime (in a concurrency-safe manner) so that the router can be changed but still get the full performance of httprouter in between swaps.

All other changes are internal!