Made UserName optional

Following
http://docs.aws.amazon.com/IAM/latest/APIReference/API_GetUser.html
The UserName argument in iam.GetUser() is optional.

In the case where the UserName is omitted, the response returns information about the user making the request. This is incredibly helpful when running code on an instance with an IAM role.

Fixes #192
Add support for setting QueryFilter conditions.
Expose query result metadata to the caller.

QueryTable's signature roughly matches that of Scan now.
fix typo
Bugfix: Return error on PutRecord
Merge pull request #211 from fantyz/master

Bugfix: Return error on PutRecord
Merge pull request #206 from hyperworks/master

fix typo
updated travis to show list of files needing gofmt
go fmt ec2.go
go fmt ec2_test.go
reformatted responses_test to make go fmt happy
Allow HTTP 206 responses from S3.

S3 returns '206 Partial Content' when passed a Range header - currently
the code mistakenly treats that as an error.
Merge pull request #215 from atlassian/fix-s3-signature

Fix s3 signature by sorting x-amz headers by their key
Merge pull request #214 from colinmarc/s3-206

Allow HTTP 206 responses from S3
Merge pull request #193 from drombosky/td-issue-192

Made UserName optional
Merge pull request #195 from nyergler/master

Support QueryFilter and query result information
add dynamodb.New()

It feels more idiomatic, and provides an obvious entrypoint to the package.
Merge pull request #216 from colinmarc/dynamodb-new

add dynamodb.New()
Merge branch 'master' of git://github.com/crowdmob/goamz into s3-friendly-proxy