Add See Also resources to README.

Mostly copy-pasted from proctor-pipet.
Add note to README about other frameworks.
Revert "Workaround nulls in Proctor API JSON."

The nulls are fixed in the latest version of proctor-pipet.

This reverts commit 613aa1e398b0c61b0a3d30420ec5d7d440ebdcee.
Fix caching matrix version via cache storage and timeouts.

The 'cache' cache method now stores the last seen version in cache.
So if one process detects a version change, all processed will
immediately pick it up and stop using outdated values.

For 'session', timeout has been added so that each process
occasionally checks with the Pipet API to make sure the matrix
version is up to date.
Updated version