3.4.0

• No model changes compared to b9
• Fixed the requirement on pixell version to 0.17.3 for reproducibility
• Added pysm_tag_filename script to add datestamp to filenames to avoid caching errors
• Added datestamp to Dust and Synchrotron templates to avoid caching errors if users had previously used a beta version of PySM 3.4.0 see commit 694653e