added description about span receivers to doc.
Add a NullScope singleton

Introduce a NullScope singleton to reduce object creation. Also adds some
methods for debugging and make trace log mode a little more helpful. Pom
version bumped to 3.0.3-SNAPSHOT.
Merge pull request #27 from ndimiduk/nullscope-singleton

Add a NullScope singleton
Merge pull request #26 from iwasakims/readme-receiver

Add description about span receivers to documentation
Upped version from 3.0.3-SNAPSHOT to 3.0.4-SNAPSHOT
Improve reliability of json parsing in graphDrawer

graphDrawer.py didn't work for me with output produced by
LocalFileSpanReceiver. This fixes the issue, but enforced the assumption of a
single span per input line.
Merge pull request #28 from ndimiduk/json-parsing

Improve reliability of json parsing in graphDrawer
Making a 3.0.4 release
Forgot to update version everywhere to 3.0.4