Test refactoring, drop support for Python 2.4
Merge pull request #79 from vmalloc/no_2.4

Require Python 2.5, major test refactoring
Updated the docs
Merge remote-tracking branch 'logbook/master'

* logbook/master:
  Test refactoring, drop support for Python 2.4

Conflicts:
	logbook/testsuite/test_contextmanager.py
	tests/test_logbook.py