Python 3

[mnaberez]

• Fix running tests on Python 3 AttributeError: 'module' object has no attribute 'test_meld3'
• Fix the package so that we can change the imports from from .meld3 back to from meld3 in a way that works on both Python 2 and 3.
• Fix test failures on Python 2.7 FAIL: test_escape_attrib_unicodeerror and FAIL: test_escape_cdata_unicodeerror
• Find why the except cause for import fixtag was changed from except ImportError: to except: and change it back if possible.
• Add tests for example.py and melddiff.py.
• Fix test failure on Python 3.3 FAIL: test_fillmeldhtmlform
• Fix test failure on Python 3.3 FAIL: test_dupe_meldids_fails_parse_xml
• Fix implementation of _encode_entity on Python 3.
• Fix test failure on Python 3.3 FAIL: test_escape_attrib_unicodeerror (related to _encode_entity)
• Fix test failure on Python 3.3 FAIL: test_escape_cdata_unicodeerror (related to _encode_entity)
• Fix warning on Python 3.3 DeprecationWarning: This method of XMLParser is deprecated...
• Update classifiers in setup.py