Add another missing mutable.
Document behaviour of join().
Ensure shutdown_context is idempotent.
Partial implementation of executor_wrapper typedefs.

Implemented argument_type, first_argument_type and second_argument_type
for plain function pointers and references.
Add pipeline example.
Remove unnecessary joinable check.
More implementation of executor_wrapper typedefs.

Implemented argument_type, first_argument_type and second_argument_type
for types that define these nested typedefs themselves.
Workaround Xcode's incomplete reference_wrapper implementation.
Fix non-boost build.
Add missing headers to makefiles.
executors version 0.1.0
Add a couple of post examples.
Add another post example.
Add more post examples.
Add actor example.
Change strand to use defer of underlying executor.
Use user-supplied allocator for scheduler, timer, strand and channel.
Use different small block recyclers for different purposes.
Use user-supplied allocator for the polymorphic executor's function objects.

If no allocator is specified, uses the small block allocator.
Merge branch 'master' of https://github.com/chriskohlhoff/executors