Narrat Syntax highlighting

Until now, narrat used .rpy files as a way to easily get syntax highlighting from another similar language.

Now, narrat has its own syntax highlighting grammar definition used to create the Narrat Language extension for Visual Studio Code.

This means narrat scripts can now use the official Narrat .narrat extension

This means that the quality of the syntax highlighting is much better, and in longer term it will be possible to add snippets, code autocompletion and other intellisense features to narrat scripting.

The extension is open source (see the GitHub repository), so it should be easy for anyone to create alternative versions of it for other text editors. The grammar is defined in the standard TextMate format.

Templates and docs updated

All the game templates and docs have been updated to reflect the change with everything defaulting to .narrat, and all references of .rpy in the docs deleted to avoid confusion.