Fixes #2730

Add documentation for numbers

JSON_VERSION_IS_PREDEFINED with JSON_HAS_CPP_11

Add support for deserialization of STL containers of non-default constructable types (fixes #2574).

Use Clang 12 in CI

Update json.hpp

Added define JSON_VERSION_IS_PREDEFINED
for skipping automatic JSON_HAS_CPP_* detection

Proposed fix for #2706

pkg-config.pc.in: Don't concatenate paths

See: https://github.com/jtojnar/cmake-snips#assuming-cmake_install_dir-is-relative-path

add more CI steps

Update doctest from 2.4.4 to 2.4.6 (fixes #2686)

License fix

Properly select "Release" build for Travis

# Conflicts:
#	.travis.yml

* ⚗ move CI targets to CMake
* ♻ add target for cpplint
* ♻ add target for self-contained binaries
* ♻ add targets for iwyu and infer
* 🔊 add version output
* ♻ add target for oclint
* 🚨 fix warnings
* ♻ rename targets
* ♻ use iwyu properly
* 🚨 fix warnings
* ♻ use iwyu properly
* ♻ add target for benchmarks
* ♻ add target for CMake flags
* 👷 use GitHub Actions
* ⚗ try to install Clang 11
* ⚗ try to install GCC 11
* ⚗ try to install Clang 11
* ⚗ try to install GCC 11
* ⚗ add clang analyze target
* 🔥 remove Google Benchmark
* ⬆ Google Benchmark 1.5.2
* 🔥 use fetchcontent
* 🐧 add target to download a Linux version of CMake
* 🔨 fix dependency
* 🚨 fix includes
* 🚨 fix comment
* 🔧 adjust flags for GCC 11.0.0 20210110 (experimental)
* 🐳 user Docker image to run CI
* 🔧 add target for Valgrind
* 👷 add target for Valgrind tests
* ⚗ add Dart
* ⏪ remove Dart
* ⚗ do not call ctest in test subdirectory
* ⚗ download test data explicitly
* ⚗ only execute Valgrind tests
* ⚗ fix labels
* 🔥 remove unneeded jobs
* 🔨 cleanup
* 🐛 fix OCLint call
* ✅ add targets for offline and git-independent tests
* ✅ add targets for C++ language versions and reproducible tests
* 🔨 clean up
* 👷 add CI steps for cppcheck and cpplint
* 🚨 fix warnings from Clang-Tidy
* 👷 add CI steps for Clang-Tidy
* 🚨 fix warnings
* 🔧 select proper binary
* 🚨 fix warnings
* 🚨 suppress some unhelpful warnings
* 🚨 fix warnings
* 🎨 fix format
* 🚨 fix warnings
* 👷 add CI steps for Sanitizers
* 🚨 fix warnings
* ⚡ add optimization to sanitizer build
* 🚨 fix warnings
* 🚨 add missing header
* 🚨 fix warnings
* 👷 add CI step for coverage
* 👷 add CI steps for disabled exceptions and implicit conversions
* 🚨 fix warnings
* 👷 add CI steps for checking indentation
* 🐛 fix variable use
* 💚 fix build
* ➖ remove CircleCI
* 👷 add CI step for diagnostics
* 🚨 fix warning
* 🔥 clean Travis