Catalog and catch the main proc macro usage error

[AS1100K]

Fixes #154

This PR also makes error with RON files much helpful as it not shows, where the error. The following is the error message generated with mistake in RON file

error: proc macro panicked
 --> examples/cu_caterpillar/src/logreader.rs:4:1
  |
4 | gen_cumsgs!("copperconfig.ron");
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: message: Syntax Error in config: Expected string at position 4:17

[gbin]

Oh yes way better!

Can you add some unit tests so we can see what types of errors it catches?

Thanks

[AS1100K]

I have added catalog of error which came to my mind and added them in tests/compile_fail directory.

Also, currently the error in the RON file is shown with line and column position only when it is an syntax error and in order to identify that a certain type exists in the RON file and in the crate would be much difficult but is possible by validating RON file in build.rs, atm I am thinking of using rustdoc-json could address this. But I believe this would be too much.

@gbin What are you thoughts on this PR?

[gbin]

@AS1100K this is awesome! We will see if the users encounter new cases but this is a really good start.