ReturnsLazily of task #256
Improved test name
Made Returns of Task to leverage new ReturnsLazily of task
added Task overload of ReturnsNextFromSequence
Added support for Returning Task<T> to ReturnsLazily overloads that take parameters
Created Task helper with FromResult methods to removed taskcompletionsource duplication

Update tests to use fluent assertions

Added missing AssertThatValueProducerSignatureSatisfiesCallSignature to Task-based ReturnsLazily with 1 argument

Fixed incorrect comment about ReturnsNextFromSequence returns null when all values in sequence have been returned

Address issues related to Tasks
Merge pull request #265 from Dashue/returnslazily_of_task

ReturnsLazily of task #256
#256 updated XML docs for new methods
corrected docs for ReturnsNextFromSequence() overloads
fixes #256
fixes #273
Merge pull request #290 from adamralph/256

256 updated XML docs for new methods