Caught with cmake --warn-uninitialized.

The name passed to find_package should match the one that is passed to
find_package_handle_standard_args, otherwise the version matching is not
properly done. The names are based on the FindXXX.cmake filename.

This also simplifies components reporting for Libevent (done by
find_package_handle_standard_args) and results in reporting a library
instead of include directory when found.

libev 4.11 seems to build fine as demonstrated by Travis with autotools.

The COMPILE_LANGUAGE generator expression is only supported since CMake
3.3. Moreover, it does not work with all generators (works with Makefile
and Ninja, but not with Visual Studio).

target_compile_options would only work if a target does not mix C and
C++ sources, since the flags are intended to be set for a specific
language, use set_source_files_properties instead. This approach is also
less repetitive.

Drop the idea of using lists and COMPILE_OPTIONS,
set_source_files_properties only understands COMPILE_FLAGS (a single
string, not a list).

Add a "check" target that builds tests before running them.

Match the output produced by autotools (libevent-client instead of
libevent_client).

Ensure that the mruby build is triggered when the surrogate "mruby-lib"
target is used. Fixes building nghttpx when mruby is missing.

`ninja nghttpx` would create the static library, but I expected a binary
`nghttpx` instead. Rename the nghttpx target to nghttpx_static and
nghttpx-bin to nghttpx.

Also fix useless MRUBY_LIBRARIES output and add the CMake build type
(e.g. Release, Debug, etc.)

libnghttp2.so was missing -fvisibility=hidden. libnghttp2_asio.so on the
other hand had hidden visibility which resulted in no exported symbols
and a broken asio client examples.

Just build a static nghttp2 library to solve this issue.

Warnings are useful, let's enable them by default.

Some detected libraries were not reported when a feature is disabled.
This change removes unnecessary second find_package calls and sets
HAVE_xxx immediately based on xxx_FOUND.

Auto-detect spdylay availability using CMake, making pkg-config
completely optional.

FindCython.cmake was taken from
https://github.com/thewtex/cython-cmake-example. The UseCython module
works, but since it is lacking an installation target setup.py will be
used instead.

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).

Need to add -fPIC to objects that will be put in a shared library.

Split the nghttp2 library into objects and a shared library from those
objects. This is needed because of symbol visibility. An advantage over
the autotools build is that there are no worries about static versus
static library builds.

Test:

    cmake $srcdir
    make nghttpx-unittest main failmalloc
    make test

Add auto-detection to the most important features (app, hpack, etc.).
Move options to a separate file for easier search.

Add cmake-based Libevent, jansson and CUnit search. Move pkg-config
handling for Libev and jemalloc to their cmake files.

Note: duplicates find_package before including CMakeOptions.txt and when
checking for features. Maybe that can be cleaned up later...

Remove build/host/target by a single target system name (CMake is
different for cross-compiling, you are suggested to set
CMAKE_TOOLCHAIN_FILE).

Fix various library variables, remove CFLAGS (INCLUDE_DIRS could be used
instead though, but I consider that minor information that could be
added later if wanted).

Fix various variable names (prefix, boost, etc.).

Might not be the best approach, maybe use thewtex/cython-cmake-example?

Avoids leaking compile flags to dependents.

Remaining work:
 - integrate mruby and neverbleed
 - integrate cunit

Must be absolute instead of relative

Do not use minus sign in macro names.

Also remove some headers which were not checked anyway and add macros to
cmakeconfig.h.in (based on the headers list in the CMakeLists.txt file).