[MRG] Fix relative imports & improve package discovery

[mohamed-ali]

Fixes #20.

As described in pep-0404:

In Python 3, implicit relative imports within packages are no longer available - only absolute imports and explicit relative imports are supported.

The solution to the recent import problems, that is compatible with both python2 and python3 is to use explicit relative import.

A more thorough discussion about this subject can be found here.

This PR:

• [x] Fixes the above import problem.
• [x] Improves package discovery.

[yahoocla]

Thank you for submitting this pull request, however I do not see a valid CLA on file for you. Before we can merge this request please visit https://yahoocla.herokuapp.com/ and agree to the terms. Thanks! :smile:

[mohamed-ali]

CLA signed.

[coveralls]

Coverage remained the same at 88.443% when pulling 1f5834d2595275642d867c43247de697a7f210e3 on mohamed-ali:fix-relative-imports into 0f17655b901e6dfabe5c2aa62b4c8e492f34b05a on yahoo:master.

[mohamed-ali]

@pumpikano could you have a look at this PR, it fixes the import problem in python3 and is compatible with both python2 & 3.