HTTP frameworks benchmark focused on D libraries

[tchaloupka]

Hi all, I've just pushed the updated results.

Test suite modifications:

* added runner command to list available tests
* possibility to switch off keepalive connections - causes `hey` 
to make a new connection for each request
* added parameter to run each test multiple times and choose the 
best result out of the runs

Tests additions:

* new RAW tests in C to utilize epoll and io_uring (using 
liburing) event loops - so we have some ground base we can 
compare against
* same RAW tests but in Dlang too - both in betterC, epoll is 
basically the same, io_uring differs in that it uses my during[1] 
library - so we can see if there are some performance problems 
(as it should perform basically the same as C variant)

Some insights:

I've found the test results from hey[2] pretty inconsistent (run 
locally or over the network). That's the reason I've added the 
`bestof` switch to the runner. And the current test results are 
the best of 10 runs for each of them.

Some results are a bit surprising, ie that even with 10 runs 
there are tests that are faster than C/dlang raw tests - as they 
should be at the top because they really don't do anything with 
HTTP handling.. And eventcore/fibers to beat raw C epoll loop 
with fibers overhead? It just seems odd..

I'll probably add wrk[3] load generator too to see a difference 
with a longer running tests.

[1] https://github.com/tchaloupka/during
[2] https://github.com/rakyll/hey
[3] https://github.com/wg/wrk