Bump version to 1.6.0.dev0
We're planning this release cycle to end in a version 2.0, but bumping
the major version will first require work to get cocotb-bus fully
removed from the code base. We'll therefore keep the the version below
2.0.0 for now and update some time during the development cycle.
# 1) we don't load dependencies by storing it in __init__.py
# 2) we can import it in setup.py for the same reason
# 3) we can import it into your module
-__version__ = '1.5.0.dev0'
+__version__ = '1.6.0.dev0'
