Add struct tags support for compiler and importer

[FabijanZulj]

Resolves #3

I did not do anything with the test runner as I am not quite sure what to do with it so tips would be appreciated

This implementation implicitly makes it so strings support backticks, not only ". If this is not an option I should extend the parser to go through Token:idents between backticks or introduce another token type only for tags, right?