[distributions] Hyper-Exponential: BOOST_MSVC -> _MSC_VER (as _MSC_VER is always defined for MS VS, whereas BOOST_MSVC isn’t defined until *after* the first call to boost/config.hpp). Also, added MSVC pragma 4389.
[distributions] Hyper-Exponential: removed 'ArgT' type requirements for constructors taking 'std::initializer_list' as argument since no more used. Also fixed a typo: 'RealTypr' -> 'RealType'.
[distributions] Hyper-Exponential: added example and doc from (Wolski et al.,2013) paper.
[distributions] Hyper-Exponential: added a note for the different results between (Wolski et al.,2013) and ours implementation. Also, improved discussion on possible accuracy issues with MATLAB/Octave.
[distributions] Hyper-Exponential: solved an issue with Quickbook's itemized lists.
Regen docs from Marco's changes.