Pyfomod

* Fix omitted destination field in `File` being the same as an empty string - it is now `None`.
* Fix multiline text not being fully parsed.

* Fix missing warning for missing info.xml file.

* Added support for `moduleImage` tag as `Image`.
* Reworked warnings:
* No longer uses the native python `warnings`;
* Warnings are now `ValidationWarning` objects;
* The `validate` functions return a list of these objects;
* You can pass a list as a keyword argument to `parse` to collect the
warnings instead of passing `quiet`;
* The user-defined callbacks for `validate` now should return a **single**
warnings object.

* Added group/option type warnings:
* SelectAtMostOne/SelectExactlyOne group with multiple required options;
* SelectAtLeastOne/SelectExactlyOne group with no selectable options.

* Added a `CriticalWarning` for non-explicit order attributes.

* `CriticalWarning`'s no longer have the extra little message at the end.
* Detected comments warning is now a `CriticalWarning`.
* Added a `CriticalWarning` for when *info.xml* is missing.
* Added a kwarg to `parse`, `lineno`, that when true provides the source
line numbers to each element object at the cost of performance.