Interface simplifications

A series of interface improvements

BREAKS THE CURRENT INTERFACE, but I think the improvements/simplifications are worth it:

• new load_budget() convenience function returns only Budget class, with ifo pre-set as class attribute.
• clean ups to gwinc() convenience function
• add Budget.run() method as simple interface to run all usual methods for common use case.

gwinc/test/__main__.py

@@ -12,8 +12,7 @@ import logging
 logging.basicConfig(format='%(message)s',
                     level=os.getenv('LOG_LEVEL', logging.INFO))
 
-from .. import load_budget
-from ..gwinc import gwinc
+from .. import load_budget, gwinc
 from ..gwinc_matlab import gwinc_matlab
 try:
     import inspiral_range