Revert commit 9e5d57c to support string tpye VERSION.
Add cmake compilation switch to choose language stanard.

Rewerite and revert some code that this library can be built in pre-C++11 and C++11 env.
Main Change List:
1. using -> typedef
2. not using auto & decltype
3. not using raw string literals
4. ..., other c++11 features will be chosen to compile, depending on env.

Improve CMake correctness and handling

This is already covered by the toplevel CMake, which also serves to
provide a consistent minimum version.

Commit aebc7faa added version checks for CMake compatibility. In reality,
only the add_compile_definitions need the check - add_compile_options
itself has been supported since 3.0. Tested and confirmed built
successfully with CMake 3.8.0.

EXTRA_CXX_FLAGS is never defined, making this a noop. Further,
COMPILE_OPTIONS is invalid to set as a DIRECTORY property.

Since the introduction of CMAKE_COMPILER_IS_GNUCXX CMake has
suggested using CMAKE_CXX_COMPILER_ID for more general checks.

Since CMake has subdirectory variable scope, unilaterally set the
CMAKE_CXX_STANDARD variable to use C++11. This covers cases with the
library being included externally, both in cases of only C++98 being
specified, as well as later versions being specified (since the
CXX_STANDARD itself isn't a library dependency, only the PUBLIC
target_compile_features on jsoncpp_lib). The previous direct check for
C++98 is handled by requiring C++11 on this library; should the
compiler being used not support C++11 then CMake will issue an error.

As of CMake 3.0 with CMP0042, MACOSX_RPATH is enabled by default.
Since the validated version used by jsoncpp is later than 3.0,
this is already covered.

The more general CMake way to handle library suffixing is to set
CMAKE_<CONFIG>_POSTFIX, so setting the Debug output suffix name should
be more correctly done by the caller or CMake configurer by setting
the desired value in CMAKE_DEBUG_POSTFIX.

* Ignore bom at the beginning of the UTF-8 text

A recent PR broken the JsonChecker tests by adding support for trailing
commas. This didn't end up breaking the build, because those tests
aren't run, except locally and only using CMake.

This patch fixes the tests by adding exclusions for trailing comma
tests, as well as updates Meson to run these tests as part of `ninja
test`.

See issue #1102.

Required to get JSONCPP_USING_SECURE_MEMORY and the SecureAllocator
available for the definition of Allocator.

commits:
ff923658c4d9f1492617557148369b34c71ba623
5907cef86ca699a842d0a8cad4c018b4da5d6e17

* [clang-tidy] remove redundant string initialization

Found with readability-redundant-string-init
Signed-off-by: NRosen Penev <rosenp@gmail.com>

* [clang-tidy] switch to raw strings

Easier to read.

Found with modernize-raw-string-literal
Signed-off-by: NRosen Penev <rosenp@gmail.com>

* [clang-tidy] fix performance issues

Found with performance*
Signed-off-by: NRosen Penev <rosenp@gmail.com>

* fix extra comma warnings

Found with clang's -Wextra-semi-stmt
Signed-off-by: NRosen Penev <rosenp@gmail.com>

* remove JSONCPP_OP_EXPLICIT

This codebase in C++11. No need for compatibility with C++98.
Signed-off-by: NRosen Penev <rosenp@gmail.com>

* remove JSONCPP_NOEXCEPT

This codebase is C++11 now. No need for this macro.
Signed-off-by: NRosen Penev <rosenp@gmail.com>

For Apple clang-800.0.42.1, which was released with Xcode 8 in
September 2016, the '=delete' on the 'is' and 'as' methods causes
the following errors for value.h:

  inline declaration of 'as<bool>' follows non-inline definition
  inline declaration of 'is<bool>' follows non-inline definition

etcetera for the other specializations of 'is' and 'as'.  The same
problem also occurs for clang-3.8 but not clang-3.9 or later.

* Prevent cmakelint warnings

Use 4 spaces for indent, no tabs

* Use ccache right

fix indents too at CMakeLists.txt

* [clang-tidy] Do not use else after return

Found with readability-else-after-return
Signed-off-by: NRosen Penev <rosenp@gmail.com>

* [clang-tidy] Convert several loops to be range based

Found with modernize-loop-convert
Signed-off-by: NRosen Penev <rosenp@gmail.com>

* [clang-tidy] Replace deprecated C headers

Found with modernize-deprecated-headers
Signed-off-by: NRosen Penev <rosenp@gmail.com>

* [clang-tidy] Use auto where applicable

Found with modernize-use-auto
Signed-off-by: NRosen Penev <rosenp@gmail.com>

* .clang-tidy: Add these checks

* Modernize meson.build

* Make tests optional
* Use `files()` for quick sanity checks

* Bump version to 1.9.3

* Bump SOVERSION, as some functions were removed
  and structs were changed, as determined by
  libabigail.

This bug is only affects platforms where `char` is unsigned.

When char is a signed type, values >= 0x80 are also considered < 0,
and hence require escaping due to the < ' ' condition.

When char is an unsigned type, values >= 0x80 match none of the
conditions and are considered safe to emit without escaping.

This shows up as a test failure:

* Detail of EscapeSequenceTest/writeEscapeSequence test failure:
/build/source/src/test_lib_json/main.cpp(3370): expected == result
  Expected: '["\"","\\","\b","\f","\n","\r","\t","\u0278","\ud852\udf62"]
  '
  Actual  : '["\"","\\","\b","\f","\n","\r","\t","ɸ","𤭢"]
  '

* use unicode code point

* change values' order, because JSONTEST_ASSERT_EQUAL(expected, actual)

* Add option JSONCPP_WITH_EXAMPLE

Allows to conditionally build examples as
it has been done for tests.  Useful for packaging.

* Do not build example by default

* tweak to avoid implicit narrowing warning.

change an int to size_t #1113

* Update main.cpp

* update testcase for reader

* add a helper function

* refactor structured error testing