implement account.update()

[gr2m]

Only username and password can be changed at this point, and only the valid session is required for authorization at this point.

---

• [x] claim this issue (@finnp)
• [x] update the README: add account.update (it is similar to account.profile.update for now)
• [x] add unit & integration test. In the latter, make sure account.username is set to the new username if it got changed, and sign out & back in with the new username / password
• [x] implement account.update()
• [x] review & merge
• [x] update https://github.com/gr2m/milestones/issues/88

[finnp]

I'm going to have a look at this.

[gr2m]

nice, all yours :+1:

[gr2m]

done via 63