Small refactoring (rename the HTTP stream parameters/variables for more clarity).
HttpServerResponse.writeBody(string) now specifies UTF-8 charset by default + default error page is written using writeBody now.
Add diagnostic metrics for PoolAllocator.
Fix AllocAppender to not reserve more memory than requested.
Trade no initial allocations vs. more allocation later on in Url().
Reduce amount of reserved memory for HTTP server request handling.