[queso/multilevel_doc-> manual] Adding all the work done on the manual about the multilevel method. It includes new description of MCMC, MC and ML, with their algorithms. New class diagrams generated by dot+doxygen, and updating Queso classes names to remove the 'uq' and 'Class'. ML method section needs reviewing.
[queso/src-> multilevel_doc] Adding documentation for MLSampling class.
[queso/src-> multilevel_doc] Adding documentation for MLSamplingOptions and MLSamplingLevelOptions classes.
[queso-> multilevel_doc] Adding the corrections Damon had the the ML section of the user's manual and a typo in MLSampling.h.
Wrapping some lines
Merge pull request #189 from dmcdougall/multilevel_doc

Multilevel doc