Update clang-format in Travis

AllowShortBlocksOnASingleLine: Empty was added in clang-format 10

Fix warning: backslash-newline at end of file

include/pistache/meson.build: Fixed missing meta.h...

Fix pkg-config usage with Meson in Readme

Add project status in the Readme

Closes #894

Reapply #890

See #890

Revert "Meson improvements"

Meson improvements

…an/control

The .pc file is now generated using Meson generator, so there's no need
anymore to store a .pc.in file in the project root and then configure it
manually. All dependencies and libraries are automatically set based on
what the build target actually uses, so there's no need to manually
track all the required libs and flags. As a result, code is much cleaner

Previously there was a check that made it possible for the users to
switch between building a static or shared library when using Pistache
as a Meson subproject. Now Meson checks for the desired library type
before defining any build targets, and if somebody wants to only use the
static library it doesn't have to also build the shared one.

Also, code is now way cleaner, since the two calls to static_library and
shared_library are now a single library() call

Move pkg-config private libraries to Libs.private

#842: Add more debug traces to http server test

Add Meson clang-format target

Since Meson doesn't have a way of specifying the working directory of a
command, I had to modify the script to make it cd into the source root
when ran from Meson.

You can run the format target with meson compile -C builddir format or
ninja -C builddir format

Fix CMake pkg-config example

Fixes #877

Add Meson support

Fix #187

\n is still used when std::endl doesn't make sense, like when using
std::cerr, since it is unbuffered.

README.md: Added link to guteksan's comparison of similar libraries...

This little PR fixes #187, while also replacing std::endl with '\n' in
the examples, since most of the time you don't want to flush the output
when outputting a newline.

...fix RapidJSON dependency, remove features from CMake

I've now implemented in Meson all the remaining features that were in
CMake, like Cppcheck and Doxygen documentation. I've also removed almost
all the non-essential features from CMake, like building examples,
documentation, code coverage, the install target, Cppcheck, and tarball
generation. This should help with maintainability, while preserving
testability, following @kiplingw and @dennisjenkins75 main concerns.

Cppcheck is not ran by default, but it is a build target; you can run it
with `meson compile -C builddir cppcheck`.

I've also made some little fixes and tweaks:

Fixed RapidJSON
dependency, as it was previously declared only as a dependency of the
run_rest_description example, while used in
include/pistache/thirdparty/serializer/rapidjson.h.

Updated CMakeLists, replacing the old Include(Dart) with the newer
Include(CTest), and also adding messaging suggesting the user to install
RapidJSON and GoogleTest on their system rather than building them from
source.

Fixed a "small" issue in meson.build, replacing add_global_arguments
with add_project_arguments, since the former can't be used in
subprojects and can cause build failures for users.