Add other benchmarks

[kelunik]

Currently it only benchmarks a plain GET /, would be interesting to see POST requests with multipart and JSON as well as larger responses with gzip / deflate.

[dbalabka]

@kelunik I will add some new benchmarks in near future.

I just found that there is an online contest of web frameworks benchmarks:
https://www.techempower.com/benchmarks/#section=data-r15&hw=ph&test=json
I would like to add similar benchmarks to this contest. Amp currently have all needed libraries to create a complete suite of a test (e.g. database drivers for PG and MySQL)

[dbalabka]

Lua script implementation for wrk POST benchmark:

1. Multipart: https://github.com/playframework/prune/blob/master/src/main/resources/com/typesafe/play/prune/assets/wrk_upload.lua
2. Urlencoded: https://github.com/wg/wrk/blob/master/scripts/post.lua