minimal tutorial updates for new api
if field value is invalid, give context in error

when supplying a wrong type of value for a field, e.g. when trying to store a long in a string, it would now just give a classcastexception within the valuetype serialization code without giving any clue as to what field contains the problematic value. Now providing more context and also added explicit check on value type.
update diagram for tables & metadata
update diagram: locks -> occ
solidify mr archetype

make the mr archetype more useful as a base for a real mr job:
 * use hadoop's ToolRunner, extend from Configured
 * don't hardcode jobtracker/filesystem config (will be picked up from hadoop config, or can be overridden with standard options -jt and -fs, explained this in the readme)
 * add solid cli parsing

Also set the job class as mainClass attribute to make it easier to launch.