llhttp does not include URL parser. We extracted URL parser code from
http-parser and put it under third-party/url-parser.
llhttp bd3d224eb8cdc92c6fc8f508d7bbe0ba266e8e92
mruby is always invoked now (mirrors the autotools behavior). It could
be optimized though to only trigger the mruby build when the static
library is missing.
Also fix typo in NGHTTP2_TESTS_DIR macro definition (detected when
invoking the Ninja generator).