make render-all public
OM-287: comprehensive pre-conditions on public API
0.8.0-beta2
bump version in README
OM-290: component? precondition unexpectedly failing

Internal we call `om.core/get-props` on a plain JavaScript object out of
a matter of convenience. Satisfy the contract.
Merge branch 'master' of github.com:swannodette/om
0.8.0-beta3