Support Python 3.5

[kwmsmith]

Related to blaze/blaze#1283

This issue will collect all tasks related to Python 3.5 support for odo:

• Pymongo 2.8 doesn't have a conda package for Python 3.5, which forces an update to Pymongo 3.0.3. My preference would be to drop Pymongo 2.8 support in odo and move to just 3.0.3, but I don't know how widespread pymongo 2.8 usage is. I'd consider supporting both 2.8 and 3.0 if the code changes aren't pervasive.

[tonyfast]

There may be some conveniences for the decorator functions using typehints.

@odo.convert.register
def convert_list( a: str )->int:
  return int(a)

is the same as

@odo.convert.register( int, str )
def convert_list( a: str )->int:
  return int(a)

I don't think this can happen until multipledispatch gets an update.

This might be a very user friendly syntax in the future. Particularly if folks start adding their own custom classes to odo.