Operator: Last

[benjchristensen]

There is already a "last" operator but Rx includes another overload:

http://msdn.microsoft.com/en-us/library/hh229203(v=vs.103).aspx

[benjchristensen]

So it appears our last() implementation is wrong and returns Observable whereas the MSDN docs show it to be blocking: http://msdn.microsoft.com/en-us/library/hh229056(v=vs.103).aspx.

This will be a breaking change to 0.5.x but needs to be done to conform to the Rx contract.

TakeLast is the correct non-blocking operator: #85

[benjchristensen]

Completed in #184 and will be released as a breaking change in 0.6.0