Consistent casing for parameters

This PR adds support for consistent, camel cased parameters (See #217).
I chose to implement camel cased names to be consistent with the AWS APIs, and because the 
alternative is to recursively check and convert snake case to camel case names - which could prove troublesome.

The following, which did not work before, works now:

```python
update_table_operation({
    'ProvisionedThroughput': {
        'WriteCapacityUnits': 2, 
        'ReadCapacityUnits': 2
    }, 
    'TableName': 'test-table'
})
```