Set version strings to 0.9.8 in source; these will be updated with major releases.
Added tools/setVersion script
setup.py now auto-generates version string based on pyqtgraph/__init__ and git info, if available
setup.py now modifies __init__.py on build to include a more descriptive version string if .git is present.
make setup.py more robust to possible errors during version string modification
Merge branch 'version_strings' into develop
* __init__.py now contains latest release version string
* installing from git checkout that does not correspond to a release commit
  will result in a more descriptive version string