Bump dependencies and version (spotify#27)

Bump the pinned dependencies and bump the package version since the
google-cloud-pubsub bump will make it (in)compatible with other Google
packages.

Remove the pinning of dev-dependencies since it is not that necessary
for a library (and they are very seldom bumped anyway).

Change the dependency of comet-core to make releases easier.

Update dependencies to use any 2.x version of comet-core (spotify#22)

Update long description format to markdown (spotify#21)

This should result in a nicer description at PyPi.
Also updated gitignore to be the same as comet-core

Fix the trove classifiers (spotify#20)

Update TravisCI and bump version (spotify#19)

* Split the toxenvs in Travis CI conf

* Bump version

Update dev environment and test all supported Python versions (spotif…

…y#18)

Update the supported Python version and how testing/linting is done

* Updates the Tox file to test for all supported Python versions.
* Adds Black as a dependency and Black test as a step in Tox.
* Adds requirements-dev.txt file with the dev requirements explicitly specified in one place.
* Configure TravisCI to run for all supported Python versions.

Bump version of comet-common to 2.1.0 and use comet-core~=2.1 (spotif…

…y#17)

move requirements to setup.py and stop pinning (spotify#14)

* move requirements to use minimum instead of pin

* move requirements to setup.py

* minor tweaks to setup.py

* pin only major

* fix lint

New exception class for comet (spotify#13)

- update pubsub input module to be able to drop invalid messages
- change LOG.exception to LOG.error in pubsub input

Version 2.0.2 (spotify#12)

- bump versions for:
  - google-api-core
  - googleapis-common-protos
  - protobuf
  - pyasn1
  - pyasn1-modules