The option `YAML_CPP_BUILD_TESTS` currently enables or disables building of tests; but unconditionally the CMake file includes CTest; this PR makes that conditional on the option.

Also, there is no option for enabling formatting, but it does check whether it can find the `clang-format` executable; this PR adds an option (default to true) that skips even looking for the executable if disabled.

After configuring the file `yaml-cpp-config.cmake.in`, the result ends up with
empty variables.  (see also the discussion in #774).

Rework this file and the call to `configure_package_config_file` according the
cmake documentation
(https://cmake.org/cmake/help/v3.22/module/CMakePackageConfigHelpers.html?highlight=configure_package_config#command:configure_package_config_file)
to overcome this issue and allow a simple `find_package` after install.

As there was some discussion about the place where to install the
`yaml-cpp-config.cmake` file, e.g. #1055, factor out the install location into
an extra variable to make it easier changing this location in the future.

Also untabify CMakeLists.txt in some places to align with the other code parts in this file.

Complies with YAML Standard [5.4](https://yaml.org/spec/1.2.2/#54-line-break-characters) [25] instead of matching `\r` only in combination with `\n`.

Fixes issue #1053.

Properly resolves #1083, #996.

Also refactor the build action to use a matrix.

Add copying of shared library to the output directory with a test binary.

[binary] removed using of non unsigned char as argument at
'std::isspace' function that was provokes undefined behavior.

[.github/workflows/build.yml] enabled run of test at the
'windows-latest' environment.

This replaces the old Travis CI badge that didn't mean anything.

Partial revert of "Revert "Revert "Hide most of non-public symbols by default (#984)" (#1038)" (#1045)"

This reverts commit 0733aeb4.

GNUInstallDirs provided may be absolute paths, in which case appending
to the install prefix is not correct. We can instead use the provided
CMAKE_INSTALL_FULL_* variables, which are precomputed absolute paths.

https://cmake.org/cmake/help/latest/module/GNUInstallDirs.html

This reverts commit da1c8d36. and fixes #1036.

* Export YAML::detail::node::m_amount

The internal header node/detail/node.h is included by public headers;
YAML::detail::node is implemented in the header itself, and thus it gets
inlined... except for its static m_amount class member, which is
instantiated in the library only. Right now all the symbols of yaml-cpp
are exported (nothing is hidden), so the linker will find node::m_amount
in the yaml-cpp library.

As solution/workaround, explicitly export YAML::detail::node::m_amount.

* CMake: use GenerateExportHeader

Make use of the GenerateExportHeader CMake module to generate the dll.h
header with export macros.

While the produced dll.h is different, the result should be the same,
i.e. nothing changes for yaml-cpp or its users.

* CMake: hide all the symbols by default

Hide all the symbols that are not explicitly exported with YAML_CPP_API.
This way the ABI will be way smaller, and only actually exposing the
public classes/functions.

Removed the variable name in the defaulted function to make GCC happy.

convert.h line130 : warning C4244 conversation from int to T possible loss of data

* fix issue743: handle the empty content of flow sep/map correctly during emitting.

* handle the empty Tag/Anchor properly.

* delete comment

- Don't eagerly convert key to std::string
- Make const char* keys streamable when exception is thrown
- Don't create a temporary string when comparing a const char* key

Fixes #917

Fixes #501

Fixes #590.

Not use 'emit' as variable name, in Qt Framework it reserved word