Feature Request: Improvements

[ricardoribas]

Hey there.

First of all, thank you for providing such library. Really useful 👍. I have some suggestions for the library. I am not sure about the best way to proceed with the feature requests and implementations. Here's the list of the improvements.

1. Prevent using reserved keywords for the property names automatically. This can easily be done by adding # or a symbol as a prefix to all the reserved words from dynamoDB (more info here). Additionally, if you add expression attribute name alias, will it be reflected on the filter expression as well?

2. Add a test data set to include test cases in order to keep up with changes and to prevent introducing new errors

3. I think the BuilderType logic is reversed. The document client is the one that requires marshalled values, and the dynamodb is the opposite. Correct me if i am wrong. For the marshalling part, you don't need to add yourself logic to it. The sdk for dynamodb already includes a helper. Perhaps there was a reason behind it.

Let me know what do you think about those changes.