N3672 Editorial Fix

Added #include <initializer_list> to the <optional> synopsis, to be
consistent with other standard headers that use initializer_list.
N3672 Bug fix

Format comma with code font in [optional.object.swap]/2.
N3672 Bug fix

Name a parameter in [optional.nullops].
N3672 Editorial fix

Only the first sentence in the Requires paragraph of [optional.hash]
is actually a pre-condition. Split the other two sentences into
paragraphs of their own, as they specify a requirement on the
implementation, not a pre-condition.
N3545 Editorial fix

Add const to the added constexpr function, as constexpr no longer
implies const, but did at the time the paper was proposed.
Bug Fix: <dynarray>, not <dynamic_array> in header overview.
[thread.general] Add header <shared_mutex> to overview table.
[thread.sharedmutex.requirements] system_error in code font
[thread.lock.shared.cons] Formatting fix.
[thread.lock.shared.cons] Formatting fix.