The old implementation did not move.

The object is never used, only its type is used.

Code cleanup:
Most of the time, values are std::moved into detail::assign,
but not always. This patch makes usage more consistent to
always use std::move, except for ints, floats, and iterators.

This tests the usage of move-only attributes.
parser.hpp and printing.hpp are slightly modified to make it work.

…e time.

The trace feature doubles the compile time, even if never used.
This patch introduces the preprocessor define BOOST_PARSER_DISABLE_TRACE
to deactivate this feature at compile time.

…is used

as a separator.

Implements #231.