Use hasattr() rather than isinstance(value, MutableSequence)

[adamcharnock]

There are several places where the code checks specifically if something is an instance MutableSequence. I believe the more pythonic way would be something like:

# rather than this
if isinstance(value, collections.MutableSequence):
# do this:
if hasattr(value, '__iter__'):

From what I can see, iterability is what is actually desired, the other functionality of MutableSequence isn't needed.

For example, I have an object which is iterable and should therefore (AFAIK) be able to be decoded into a collection. However, right now it fails the check for being a MutableSequence.

This is potentially an extension of issue #18 from last year.

[adamcharnock]

Just updated to fix issues due to strings in python3 being iterable.

[jaimegildesagredo]

Hi @adamcharnock and thank you for the PR.

Just let me review if these changes have any other implication (specially the isinstance statements) before merging it.