Update badges in README

Use `dtoa()` for optimal encoding of reals

Simplify tests even more

Drop the useless `export` lines from `env` files.

Refactor tests

Use sprintf() to determine locale's decimal point

This should fix thread safety of encoding and decoding, since
localeconv() is not tread safe after all.

Bump the github-actions group with 1 update

Bumps the github-actions group with 1 update: [actions/upload-artifact](https://github.com/actions/upload-artifact).


Updates `actions/upload-artifact` from 3 to 4
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](https://github.com/actions/upload-artifact/compare/v3...v4

)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: github-actions
...

Signed-off-by: dependabot[bot] <support@github.com>

Add dependabot, update GitHub Actions

Ditch coveralls

Signed-off-by: Pedro Kaj Kjellerup Nacht <pnacht@google.com>

Signed-off-by: Pedro Kaj Kjellerup Nacht <pnacht@google.com>

Remove unused ${SOURCE_DIR}/include include path

The directory `${CMAKE_CURRENT_SOURCE_DIR}/include` is never created or used. Except in case of an in-source build but then  `${CMAKE_CURRENT_BINARY_DIR}/include` would be the same, so it would only duplicate the correct entry.

Not sure if the intermediary `JANSSON__INCLUDE_DIRS` is still necessary but I thought I'd change as little as possible.

The reason for eliminating this is that when you use CLion and sync into a docker container it will try to copy all include dirs back. Non-existant paths cause warnings every time.

fix typo

Signed-off-by: lilinjie <lilinjie@uniontech.com>

hashtable: change to ifdef

All other usages use ifdef.

Add a missing json_decref in the example

Fix overwriting linker flags