examples: Add tiny-nghttpd

tiny-nghttpd is HTTP/2 server and its purpose is measure the
performance of nghttp2 library code.  Currently it only accepts direct
HTTP/2 connection only.
examples: Build tiny-nghttpd only when epoll is available
nghttp2_hd: Search dynamic table first

Since recently used headers are in dynamic header table, it is
advantageous to search dynamic table first, saving time to search
through static table.
Check Boost library only when it is requested
examples: Fix travis error: unreachable-code
libnghttp2_asio: Add request::run_task to execute task in separate thread
libnghttp2_asio: Move common types and functions to nghttp2::asio_http2 ns
doc: Add example to use nghttp2::asio_http2::server::request::run_task
Update doc
Fix `make distcheck`
Bump up version number to 0.6.2, LT revision to 6:0:1
Update man pages
Bump up version number to 0.6.3-DEV