Changes based on Boost review feedback and other improvements

This release incorporates the feedback of the Boost Review, changes to improve potential integration with Boost, simplified asynchronous API. Changes:

• The is_e_type trait is deleted. Any value type can be used as an error type.
• Error handlers can now be captured in a tuple and used with try_handle_some, try_handle_all or try_catch. The remote_ prefixed error handling functions are removed.
• preload, defer, and accumulate are all merged into a single API called on_error.
• match is now compatible with std::error_code, e.g. match<std::error_code, 42>.
• Error handlers that take arguments of exception types will automatically catch exceptions; catch_ is now optional, primarily used to catch more than one exception type.
• Error handlers can now take mutable reference (and mutable pointer) arguments.
• augment_id is renamed to error_monitor.
• All LEAF_XXXX macros are renamed to BOOST_LEAF_XXXX.