Feature/perfutil

This PR tries to solve part of #10 (but more oriented towards performance tests than load tests).

With the refactoring of the last few days, the tests are now running in 2.5 seconds on my Windows VM, mostly by turning off super-verbose logging, and we are in a good position to start using PerfUtil and Fuchu for solving #10.

For my own mental sanity, I've also done a lot on #82 to remove the number of visible functions per module. Mostly I've moved stream, byte and string parsing functions to the Util namespace and split the tests into separate modules while keeping the shared tests functions in a new 'TestUtilities.fs'.