Wrap the full descriptive text for both classes in a QuickBook template
parameterized with class name and appropriate substitutions for the (few)
differences between the two classes.
Note effect of BOOST_USE_SEGMENTED_STACKS if StackAllocator is not explicitly
passed.
Introduce function_heading_for QuickBook template to allow separate
descriptions of swap(fiber), swap(packaged_task) and swap(promise).
Document async() using C++14 std::result_of_t and std::decay_t, aligning with
std::async() documentation.
Rework when_any / when_all examples to use unbounded_channel throughout, since
we always close() the channel after the first value anyway. bounded_channel
doesn't really add much value here.
Make wait_first_outcome_impl() infer its channel pointer type. That way we can
reuse that function instead of coding a separate wait_all_until_error_impl(),
which differs only in using the nchannel facade instead of directly pushing to
unbounded_channel.
Explain use of std::bind() to bind a lambda.
Use a more nuanced discussion of promise lifetime in write_ec() example
function.
Use condition_variable::wait(lock, predicate) in a couple places in
work_sharing.cpp example.
Add a note to the condition_variable::wait_for(..., pred) overload.
fiber_specific_ptr::reset() has no default argument.
Remove mention of launch policy deferred, since no API accepts a launch
policy argument.
Copy construction or copy assignment of a shared_future leaves other.valid()
unchanged. It won't be 'true' unless it was 'true' before.
Mention that [shared_]future::get_exception_ptr() does not invalidate.
Note that 'blocks' and 'suspends' are used interchangeably.
Add some cross-references; add link to std::allocator_arg_t. Clarify the
cross-reference to the paragraph describing BOOST_FIBERS_NO_ATOMICS.
Reformat some overly-long source lines.
