Include the source location in diagnostics

[stephenatwork]

#92 duplicates output to the debugger output window.

If file:line number info was added, one could click on the issu & go to the source.

[tritao]

I've looked into adding SourceLocation support to the AST before to improve the diagnostics (and have one-click support to go to the sources in VS) but did not end up finishing it. I will take another stab at it.

[tritao]

Declarations now keep track of their location, diagnostics stil need to be enriched with this information.