Issue 318 Support for DynamoDB and delegation to Inflector of case conversions

Been working on making DynamoDB work with php-activerecord.  ATM you can mix in DynamoDB as another data source....relationships from DynamoDB to SQL records generally work ok.  Naturally a lot of sql options are not supported.

This also removes a huge number of strtolower calls all over the place and delegates the specification of pdo_dboptions to the inflector, which should be the sole converter of names in the library.  It also introduces a NullInflector because I don't care for inflectors and more to the point.....I need to produce JSON that case matches the case used by the fields in the database and lowercasing stuff everywhere makes this impossible.  So pluggable inflectors are available for people who like how it works now....but also hackable for people like me who need the case not to be messed up.