Breaking changes

Compared to version 1.0.0:

• ITranslator and II18Next have new members (ExistsAsync, TranslateObjectAsync, TObject, T<TModel>, ...). Custom implementations have to add them.
• Newtonsoft.Json was replaced by System.Text.Json.
• TranslationTree.GetAllValues() returns the full key paths (look.deep instead of deep).
• Translating a key which leads to an object returns i18next's key '...' returned an object instead of string. message instead of throwing an exception.
• JSON v1 plural suffixes for numbers use _plural_N like i18next and negative counts use the absolute value.
• TraceLogger respects its LogLevel.
• .NET Standard 2.1 and .NET 5 are no longer separate targets, they use the .NET Standard 2.0 build.
• DefaultInterpolator.HandleRegexMatch and HandleUnescapeRegexMatch were removed, interpolation runs in a single pass. Override GetValueForExpression or EscapeValue to customize values.
• Values inserted by interpolation are not interpolated or nested again (SkipOnVariables, like i18next).
• CompositeBackend is obsolete, use ChainedBackend.
• The missing key event is raised once per language, fallback languages equal to the requested language are skipped.
• uppercase and lowercase are handled by the DefaultFormatter without registering a formatter.
• Numbers inserted without a format are written culture invariant like in i18next (1.5), use {{value, number}} for localized numbers.