Add dynamodbattribute.ConvertX to wiki

[jasdel]

New converts were added to dyanmodb service package to make AttributeValue usage more user friendly. Information about these converts should be added to our wikis. Should probably include package doc line, and a few examples in code comments for godocs.

godocs for dynamodbattribute.ConvertX

Related to #125, #231

[jyehbrightcove]

I noticed that the library is located at:
github.com/aws/aws-sdk-go/service/dynamodb/dynamodbattribute

It looks like the package declaration is dynamodb, which is the same as the parent folder. Was this intentional? If I try to import both this and the parent, I get a complaint that dynamodb is being redefined.

I figured I might be missing something so I didn't want to raise an issue at first.

[lsegal]

@jyehbrightcove I just merged a pull request #285 that resolves this, thanks for reporting!

[jyehbrightcove]

My apologies for not looking at the outstanding PRs.

[jasdel]

Documented the functionality via the package doc along with examples.