Add missing preprocessor key words

[gep13]

Currently, within the CakeLanguage file, we include the following:

https://github.com/cake-build/cake-vs/blob/develop/src/Classifier/Languages/CakeLanguage.cs#L14

public static List<string> Preprocessors => new List<string> {@"^[#]{1}(load|r|addin|tool)"};

However, as per the docs here:

https://cakebuild.net/docs/writing-builds/preprocessor-directives

There are actually other directives that we should support.

[gep13]

A PR was opened to address this issue:

#85

But this will require to be updated, with the recent changes that were made to the source code.