Doxygen comments for NuPIC.hpp and Network.hpp.
Link docs
Added Input docs with types
Doxygen comments for Output.hpp.
Merge pull request #507 from rhyolight/nupic-network-docs

Doxygen comments for NuPIC.hpp and Network.hpp.
Merge pull request #508 from rhyolight/link-output-input-docs

Link output input docs
Merge branch 'master' of https://github.com/numenta/nupic