Release tagging

[hartytp]

In setting up a Conda package for quamash (OxfordIonTrapGroup@b006c9a) I hit two issues:

1. Currently releases are tagged using the pattern version-x.y.z. The hyphen upsets my build script.
2. Currently, setup.py doesn't run without a GUI toolkit installed.

AFAICT (2) will be fixed by #111 Would you be open to changing the tagging format for future releases to something like vx.y.z to resolve (1)?

[hartytp]

@harvimt Are you interested in having a Conda build for quamash? If so I'm happy to submit a PR