(! means necessary / blocker for releasing v3)

# General changes:

# Github:
X Update branch names on Github (rc3 -> v3)
X Create a new release on Github

# Website:
X Update website:
  X Finalize changelog
  X Update installation instructions
  X Remove " ITensor version 3 has not been released yet. This documentation is a preview only."
  X Make v3 the default in the docs system
  X Update code samples of DMRG and contraction on the main page
  X Update news
  X Update front page, including news article link

X Send email

X Post about v3 on ITensor Twitter account

# Final Release Checks
  X Fresh install with new options.mk file compiles
  X All sample codes compile and run and are up to date
  ! Jenkins is passing