Hello @borntyping,

First of all, thank you for putting all the effort into this project - it's the best Riemann Python client out there.

This PR includes several small fixes, that make it easier for me and my colleagues to use the project (plus an unrelated fix to the readme):

• Using relative imports lets the user decide how the module is named (comes handy when you're vendoring the package).
• Adding all public classes to init takes away some of the repetitiveness in the imports (e.g. from riemann_client.client import Client). If need be, this also lets you refactor the package structure more easily, as it all appears flat to the caller.

from riemann import Client as RiemannClient

with RiemannClient() as client:
    event = {...}
    client.send(**event)

• Make the command-line program executable with python -m riemann_client. This is also necessary for riemann_client to work as a zipapp.

Kind regards,
Georgi