Some API processing is very slow (e.g., getaddrinfo).  To avoid to
slow down regular request handling, if multi threaded configuration is
enabled, we allocate dedicated worker for API.

This function sets the maximum length of header block (a set of header
fields per HEADERS frame) to send.  The length of given set of header
fields is calculated using nghttp2_hd_deflate_bound().  Previously,
this is hard-coded, and is 64KiB.

h2load has supported uploading a file quite a while, but it turns out
that it worked with HTTP/2 and SPDY only.  HTTP/1 with upload did not
work.  This commit fixes this bug, and implement HTTP/1 upload.  Due
to architectural limitation of h2load, when -d option is used, the
number of in-flight pipe-lined requests is set to 1.

Suppose the wildcard patterns follows:

- *.nghttp2.org/foo
- *.img.nghttp2.org/bar

Previously, s.img.nghttp2.org/foo does not match anything.  Now it
matches first pattern.