Fix issue #115

Moved "bailout" code to the top of the Filter.filter method, so it catches empty list and tuple.
Ammended my fix for #115

Instead of moving bailout code, added condition on list length, to prevent unpacking of empty list.
Fixed test models for python3.x
Added exclusion filters support
Address passing lookup type to tilter method.

LookupTypeField.compress() now returns Lookup (a simple namedtuple) instance.
Filter.filter() now checks for value being a Lookup instance and handles setting lookup_type
Adjust tests to handle these changes.

Fixes: #115
Fix typo in LookupTypeField.compress.
Merge pull request #116 from augonis/develop

Fix issue #115
Updated docs for generic view from "filter_class" to "filterset_class" as expected.
Fix some formatting in docs.

The indentation was causing the whole block to render as a `<pre>`.
Merge pull request #122 from meshy/patch-1

Fix some formatting in docs.
Merge pull request #120 from Ogreman/patch-1

Updated docs for generic view from "filter_class" to "filterset_class" as expected.
Merge pull request #100 from noirbizarre/exclude

Allow exclusion filter
Add warning about lookup type for CharFields/TextFields

I had an issue with it and #django IRC said that it's quite common issue so... here we go!
Fix line-lenght
Fix typo in widgets docs
Merge pull request #129 from chuwy/patch-1

Fix typo in widgets docs
Merge pull request #125 from daGrevis/patch-1

Add warning about lookup type for CharFields/TextFields
Updates README file
Adds DateTimeRangeFilter and DateTimeRangeField
Adds citation on doc