PLT-557 - Add extra methods to Result to handle collections of results

- Added ``combine`` and ``flatCombine`` methods, together with code
samples in the javadoc.
- Added tests to show usage
- Minor other fixups to javadoc
PLT-557 - Add extra methods to Result to handle collections of results

- Standardize static imports
PLT-557 - Add extra methods to Result to handle collections of results

- address review comments
PLT-557 - Add extra methods to Result to handle collections of results

- address review comments
PLT-557 - Add extra methods to Result to handle collections of results

- address review comments
Merge pull request #40 from OpenGamma/topic/PLT-557

Topic/plt 557