Things required to build loader for Mortar to use.
Fix byte arrays being loaded into pig
Improve handling of maps by doing some basic type checks (instead of just loading everything as a bytearray)
Add basic mortar readme
* Support all data types when loading without a schema
* Support declaring an array as a tuple if you provide the correct number of items.
* Clean up some code
Support _id in a schema by changing it to underscore_id in Pig (since Pig doesn't support fields starting with "_").
remove unnecessary log message and propagate cause in new exception. 
Merge pull request #4 from mortardata/jkarn_better_map_loading

Jkarn better map loading