Remove tests from production code

[escodebar]

Remove find_packages and add engineio packages

...to prevent the tests to be included in production code.

From "Using find_packages()":

For simple projects, it’s usually easy enough to manually add
packages to the packages argument of setup(). However, for very
large projects (Twisted, PEAK, Zope, Chandler, etc.), it can be a
big burden to keep the package list updated. That’s what
setuptools.find_packages() is for.

Read:
https://setuptools.readthedocs.io/en/latest/setuptools.html#using-find-packages

Resolves #123

[escodebar]

I changed the previous commit, because removing the __init__.py lead to tests not being found by python setup.py test. This new implementation prevents the tests from appearing in the production (installed) code and allows python setup.py test to find the test files (and therefore collect the tests).

[miguelgrinberg]

Thanks!