Not working:
 - option(... check)
 - not finished everything (see XXX and FIXME)
 - still halway converting

`go test` requires both config.go and the test files in the same
directory. For out-of-tree builds, config.go is normally not placed next
to the source files, so copy the tests to the build directory as a
workaround.

Fixes multiple errors while making docs:

    Could not import extension sphinxcontrib.rubydomain (exception: No module named 'sphinxcontrib')

and

    ../../doc/sources/index.rst:15: WARNING: toctree contains reference to nonexisting document 'nghttp.1'
    ../../doc/sources/index.rst:15: WARNING: toctree contains reference to nonexisting document 'nghttpd.1'
    ../../doc/sources/index.rst:15: WARNING: toctree contains reference to nonexisting document 'nghttpx.1'
    ../../doc/sources/index.rst:15: WARNING: toctree contains reference to nonexisting document 'h2load.1'
    ../../doc/sources/index.rst:15: WARNING: toctree contains reference to nonexisting document 'programmers-guide'

Fixes the following two warnings:

    examples/client.c:292:0: error: macro "MAX_OUTLEN" is not used [-Werror=unused-macros]
    examples/tiny-nghttpd.c:298:13: error: function declaration isn’t a prototype [-Werror=strict-prototypes]

Caught using cmake as the autoconf check fails due to unused macros
(HAVE_xxx in conftest.c) and a main function without parameters
respectively.

Only used by lib/nghttp2_npn.c where the presence of config.h does not
seem to make a difference though.

Document compiling apps and include h2load in configure