improve scaladoc generation

- turn on source linking in scaladoc and link to git tree on GitHub via tags, using the -sourcepath and -doc-source-url flags
- build an api mapping for http://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/
- fix javadoc links using http://stackoverflow.com/a/25070934
Merge pull request #20 from pellucidanalytics/topic/scaladoc

improve scaladoc generation