set QuakeML-valid resource identifiers on init
don't initialize a new ResourceIdentifier for event classes if
`resource_id=False` is specified
handle the forced initilization of resource_id via kwarg
documentation for previous change
Merge branch 'master' into event_set_resource_id_on_init
positional args should better be avoided in event type classes from
class factory
don't know why this was found to cause problems in 1dc4f92a3950 but on
current python 2.7 lists of lines should go into difflib (and not one
long string)
fix (doc)tests, fix resource_id handling when reading a Comment
dont force new ID on clear()
Merge pull request #661 from megies/event_set_resource_id_on_init

set QuakeML-valid resource identifiers on init
Attempt at refactoring cfrequency
Attempt at refactoring cfrequency
Added test for non windowed cfrequency
PEP8
correcting docstring in gse2.paz.readPaz

closes #672
The ResourceIdentifier class now also tracks each single reference.

This enabled some logic to automatically remove links from resource ids
that go out of scope and get garbage collected. Also added some tests
for it.

Previously the resource ids have been been valid as long as the object
they point at exists, even if the resource identifier no longer existed.
Now it works both ways.

Also added a setUp method to the event test suits resetting the
ResourceIdentifiers.
Removing the property deletion method of the resource_id.

It only raised an error which is what also happens if it is not
present...
Changing properties to use a decorator
Merge pull request #671 from amaggi/fix-cfrequency-refactoring

Fix cfrequency refactoring (fixes #532)
Changes to error reporting when assiging non-hashable types as a resource id