Fix #85: Improve inventory helper, avoid NPEs

Adding NPE checks so we just no-op and don't crash.
Also improving checkForDoubleChest to not check up/down and to check for
null TEs
(0.2.13A2) Minor version upgrade
Fix #88: Use isAirBlock instead of Material.air

Also, add better error messages for validation problems!
Fix TiCo ender giving wrong amounts of energy

Whoops. Execution-order problem.
(0.2.14A) Version bump & changelog update
Merge remote-tracking branch 'origin/master' into dev