Add support for loading from serialized Json & Yaml strings

[radj307]

I needed to be able to load translations directly from embedded resources in an assembly without writing them to the disk. Currently, it isn't possible to use the built-in JsonFileLoader & YamlFileLoader to manually load from non-file sources.

This PR implements methods to support loading translations directly from serialized strings, to allow using the parsing capabilities of the built-in file loaders without an actual file.

• Added LoadFromString to JsonFileLoader.cs
• Added LoadFromString to YamlFileLoader.cs
• Renamed fileName parameter in ParseSubElement to source to better describe its purpose (the name also matches the source parameter in LocalizationLoader.AddTranslation)
• Fixed comments in YamlFileLoader.cs referring to Json format

Usage example:

string serializedJson = "..."; //< this can come from a stream, file, or anywhere else you can get data from

var jsonFileLoader = new JsonFileLoader();
LocalizationLoader.Instance.FileLanguageLoaders.Add(jsonFileLoader);

jsonFileLoader.LoadFromString(serializedJson, LocalizationLoader.Instance);

[codingseb]

Hello @radj307, Thanks a lot for this nice Pull request. The possibility to load from string is very useful.

I merge already this and it will be include in next release.