Optional: fix some unused parameter warnings
Remove extra :'s.  Fixes #7973.
Some doc typos.  Fixes #7602.
Correct definition of operator unspecified-bool-type.  Make reference for is_initialized point to this operator.  Fixes #6364.
Replace deprecated function reset in examples.  Fixes #765.
Work around msvc bug when explicitly destroying a class with a virtual base.  Fixes #5940.
Use __may_alias__ instead of may_alias.  Fixes #6410.
Add a forward declaration of the ostream operator for optional.  Fixes #2103.
Update optional documentation.
Try to fix VC8.