Also run clang-format on these files as requested

Add empty list of sources to add_library and add_executable.

The generator expressions here are actually unnecessary, now that I think about it.

This should fix #745

Example of how someone might consume yaml-cpp with bazel:

cc_binary(
    name = "example",
    srcs = ["example.cc"],
    deps = ["@com_github_jbeder_yaml_cpp//:yaml-cpp"],
)

Remove 2.6-isms
Remove 2.8-isms
Bump CMake minimum version to 3.4

Disable some options when used as a subdirectory

Use `CONFIGURE_DEPENDS` with `file(GLOB)` when possible

Backport CMake 3.15's MSVC_RUNTIME_LIBRARY setting.
Set all compile options as generator expressions.
Set all find-package files to be installed to the correct file.

Remove `export(PACKAGE)`, as this has been deprecated.
Remove fat binary support
Remove manual setting of iPhone settings. These should be set by parent
projects.
Remove use of ExternalProject for a local use
Conditionally remove format target unless clang-format is found

* CMake: Prefix options with "YAML" and hide platform-specific options

When including yaml-cpp as a subproject, some option names can conflict with other projects.

(1) Make sure the yaml-cpp options are prefixed with YAML
(2) Hide platform-specific options when possible to avoid cluttering the cmake option list

* Update docs for change from BUILD_SHARED_LIBS to YAML_BUILD_SHARED_LIBS

Setting CMAKE_CXX_STANDARD and CMAKE_CXX_STANDARD_REQUIRED directly is problematic when including yaml-cpp as a subproject.

The proper way is to set these per-target.

This sets the other variables:

 https://cmake.org/cmake/help/latest/command/project.html

Specifically, printing `.nan`, `.inf`, and `-.inf`, respectively, as per the spec section 10.2.1.4.

Invalid access via operator[] or as<> will now print the offending key, if possible.

For example:

a:
  x: 1
  y: 2

node["a"]["z"].as<int>()

will say that the key "z" was invalid.

It wouldn't have compiled anyways, since the Scanner and Directive objects inside it are incomplete types at the time of the move definitions.

* Add compilation flags: -Wshadow -Weffc++ -pedantic -pedantic-errors
* Delete implicit copy & move constructors & assignment operators
  in classes with pointer data members.
* An exception to the above: Add default copy & move constructors &
  assignment operators for the Binary class.
* Convert boolean RegEx operators to binary operators.
* Initialize all members in all classes in ctors.
* Let default ctor delegate to the converting ctor in
  Binary and RegEx
* Don't change any tests except regex_test (as a result of the change
  to binary operators).

Note: https://bugzilla.redhat.com/show_bug.cgi?id=1544675 makes
-Weffc++ report a false positive in "include/yaml-cpp/node/impl.h".

ref #110

NDK now uses ninja for building but yaml-cpp would emit the “ninja: error: build.ninja:326: bad $-escape (literal $ must be written as $$)” error due to syntax error in the generated build.ninja file. Related issue: https://github.com/jbeder/yaml-cpp/issues/630

Splitting the condition of the if statement containing `constant expression` eliminates warnings in Visual Studio with /W4.

The issue is that numbers like
2.01 or 3.01 can not be precisely represented with binary floating point
numbers.

This replaces all occurrences of 'std::numeric_limits<T>::digits10 + 1' with
'std::numeric_limits<T>::max_digits10'.

Background:
Using 'std::numeric_limits<T>::digits10 + 1' is not precise enough.
Converting a 'float' into a 'string' and back to a 'float' will not always
produce the original 'float' value. To guarantee that the 'string'
representation has sufficient precision the value
'std::numeric_limits<T>::max_digits10' has to be used.

* Removed an expression which is always true
* The second expression (ch is space) is removed because the first one contains space 0x20
* nextEmptyLine is always false so it is removed from the expression

Let CMake handle the default optimizations for various configurations. We don't need to override them. In fact, overriding them makes it impossible for users to override them themselves.

- Option defaults to ON and setting it to OFF, disables install
  target generation

* fix up static, so works as DLL

Variable "it" was shadowed

* Skip newlines in binary decoding
This fixes #387

* Skip all whitespace characters

This also removes spaces and tabs in addition to newlines.

Roll-forward of c90c08cc "Revert "Improvements to CMake buildsystem (#563)""

NEW:

* Replace CMAKE_SOURCE_DIR with CMAKE_CURRENT_SOURCE_DIR

Fixes #612 when yaml-cpp is used as a git submodule.

ORIGINAL:

* Move enable_testing() into proper place

* Added CMake's checks for C++11 standards

Raised minimal version of CMake to 3.1, since on old systems there no
decent compilers that supports c++11.

Closes #377.

* Externalize googletest project

Externalize gtest to avoid installation, fixes #539.

* Remove defined cmake_policies

CMP0012 - OLD marked as deprecated for >=cmake-3.1 and will be removed
CMP0015 - does not affect to build process
CMP0042 - already NEW for >=cmake-3.1

Fixes #505

* Fix compiling in Windows MSVC