Rapidyaml

New features & improvements
- Enable parsing into nested nodes ([87f4184](https://github.com/biojppm/rapidyaml/commit/87f4184))
- `as_json()` can now be called with tree and node id ([4c23041](https://github.com/biojppm/rapidyaml/commit/4c23041))
- Add `Parser::reserve_stack()` ([f31fb9f](https://github.com/biojppm/rapidyaml/commit/f31fb9f))
- Add uninstall target ([PR 122](https://github.com/biojppm/rapidyaml/pull/122))
- Update [c4core](https://github.com/biojppm/c4core) to v0.1.1
- Add a [quickstart sample](samples/quickstart.cpp) with build examples.
- Update [README.md](README.md) to refer to the quickstart
- Add [gdb visualizers](src/ryml-gdbtypes.py)
- Add `SO_VERSION` to shared builds

Fixes
- Fix [139](https://github.com/biojppm/rapidyaml/issues/139): substr and csubstr not found in ryml namespace
- Fix [131](https://github.com/biojppm/rapidyaml/issues/131): resolve references to map keys
- Fix [129](https://github.com/biojppm/rapidyaml/issues/129): quoted strings starting with * parsed as references
- Fix [128](https://github.com/biojppm/rapidyaml/issues/128): segfault on nonexistent anchor
- Fix [124](https://github.com/biojppm/rapidyaml/issues/124): parse failure in comments with trailing colon
- Fix [121](https://github.com/biojppm/rapidyaml/issues/121): preserve quotes when emitting scalars
- Fix [103](https://github.com/biojppm/rapidyaml/issues/103): ambiguous parsing of null/empty scalars
- Fix [90](https://github.com/biojppm/rapidyaml/issues/90): CMAKE_CXX_STANDARD ignored
- Fix [40](https://github.com/biojppm/rapidyaml/issues/40): quadratic complexity from use of `sscanf(%f)`
- Fix emitting json to streams ([dc6af83](https://github.com/biojppm/rapidyaml/commit/dc6af83))
- Set the global memory resource when setting global callbacks ([511cba0](https://github.com/biojppm/rapidyaml/commit/511cba0))
- Fix python packaging ([PR 102](https://github.com/biojppm/rapidyaml/pull/102))

Special thanks
- Gei0r
- litghost
- mithro
- costashatz

This is the first ryml release. Future releases will have a more organized changelog; for now, only recent major changes are listed.

Please be aware that there are still some anticipated breaking changes in the API before releasing the 1.0 major version. These are highlighted in [the repo ROADMAP](https://github.com/biojppm/rapidyaml/blob/v0.1.0/ROADMAP.md).

* 2020/October
* [MR89](https://github.com/biojppm/rapidyaml/pull/89):
* fix python API generation in windows
* use github actions for testing and releasing
* [MR88](https://github.com/biojppm/rapidyaml/pull/88): [fix MacOS compilation and installs](https://github.com/biojppm/rapidyaml/issues/75). This is a fix from [c4core](https://github.com/biojppm/cmake/issues/1).
* [MR88](https://github.com/biojppm/rapidyaml/pull/88): [fix boolean handling](https://github.com/biojppm/rapidyaml/issues/74). This is a fix from [c4core](https://github.com/biojppm/c4core/pull/18/). `true` and `false` are now parsed correctly into `bool` variables:
c++
auto tree = parse("{foo: true, bar: false}");

Emitting `bool` variables still defaults to `0`/`1`, like the default behaviour in the STL. To explicitly request `true`/`false` use `c4::fmt::boolalpha()`:
c++
node << var; // "1" or "0"
node << c4::fmt::boolalpha(var); // "true" or "false"

* 2020/September
* [***Breaking change***] [MR85](https://github.com/biojppm/rapidyaml/pull/85) null values in YAML are now parsed to null strings instead of YAML null token "~":
c++
auto tree = parse("{foo: , bar: ''}");
// previous:
assert(tree["foo"].val() == "~");
assert(tree["bar"].val() == "");
// now:
assert(tree["foo"].val() == nullptr); // notice that this is now null
assert(tree["bar"].val() == "");

* [MR85](https://github.com/biojppm/rapidyaml/pull/85) Commas after tags are now allowed:
yaml
{foo: !!str, bar: ''} now the comma does not cause an error

* [MR81](https://github.com/biojppm/rapidyaml/pull/81): Always compile with extra pedantic warnings.
* 2020/May
* [***Breaking change***] the error callback now receives a source location object:
c++
// previous
using pfn_error = void (*)(const char* msg, size_t msg_len, void *user_data);
// now:
using pfn_error = void (*)(const char* msg, size_t msg_len, Location location, void *user_data);

* Parser fixes to improve test suite success: [MR73](https://github.com/biojppm/rapidyaml/pull/73), [MR#71](https://github.com/biojppm/rapidyaml/pull/71), [MR#68](https://github.com/biojppm/rapidyaml/pull/68), [MR#67](https://github.com/biojppm/rapidyaml/pull/67), [MR#66](https://github.com/biojppm/rapidyaml/pull/66)
* Fix compilation as DLL on windows [MR69](https://github.com/biojppm/rapidyaml/pull/69)