use `@property` decorators instead of `set_` and `get_` methods

[davemfish]

It's arguably more pythonic to always set attributes through assignment rather than with a method call.

resource.title = 'foo'

instead of,

resource.set_title('foo')

Both work now, so the proposal here would remove the set_title interface and force use of the former. The benefit of this is that we can make future changes to the setter function without breaking any user code.

For more complicated attributes we might want to keep methods like set_field_description and set_band_description.

I don't think we should make any changes right away, but should keep this issue in mind as we do #29 , since that issue might necessitate some refactoring also.

[davemfish]

on hold because I haven't thought about this in a while and want to re-affirm that it is a good idea before doing it.