Release 0.4.0

As decided on maintainers meeting of 2021-03-25, we will:

• reserve 0.3.0 for releasing "Qblox and ZI backends" and prioritize that (!49 (merged) )
• push "program flow control" developments to future sprints 0.4.0/0.5.0

---

TODO for 0.4.0/0.5.0:

• Program flow

  • ControlStack (!70 (merged) )
  • QCoDeS Paramters integration with Schedules (@AdriaanRol developed prototypes of this)
  • Schedule acquisition return types (@AdriaanRol, please confirm that i specified it correctly)
  • Integrations with MC

• DOCUMENTATION - we lack a lot of it!

---

There are several related issue #66 (closed) #67 (closed) #68 (closed) #78 (closed) #79 (closed) #81 (closed) (and probably more)