Fix 0.8.1 regression in ROOT_URL with path

Fixes #2109.
Add credential secret argument to `retrieveCredential` functions.

Fixes #2118.
Unregister sessions from server when their heartbeats time out.

Conflicts:
	History.md
Update History.md
Make a History sentence more sentence-y
Update banner and notices
Update docs to 0.8.1.2
Update examples to 0.8.1.2
Merge branch 'release-0.8.1.2'