Moving Stream Fusion details into its own section. 

This level of detail does not belong in the introduction.
Merge branch 'master' of github.com:xich/hermit-opt-haskell13
Reworking intro (again).
Merge branch 'master' of github.com:xich/hermit-opt-haskell13
Merge branch 'master' of github.com:xich/hermit-opt-haskell13