Adjust Throughput Minimums

AWS recently announced that you are now allowed to set a minimum of one throughput unit for read and one throughput unit for writes. I've been using it in my pure-boto implementation for a while now.

Was hoping you guys would update https://bitbucket.org/maxnoel/dynamodb-mapper/src/408df5002c3c/dynamodb_mapper/model.py#cl-323 and remove the check since this is now valid.

Original bug report: https://bitbucket.org/maxnoel/dynamodb-mapper/issue/1/adjust-throughput-minimums by @Randall Degges

We have a pending Pull request related to this bug. I will work on it today.

merge @Kim Scheibel changes, close #12, update tests + changes

→ 36a20fad7989

Fix will be in next release (1.7.0), thanks for reporting.