Add from_bare_hash to Fieldmapper.pm.

Add from_bare_hash to Fieldmapper.pm.

Teach the Perl Fieldmapper.pm to build objects from a hashref in a
similar manner to how the JS Fieldmapper already can.  You might use
it if you retrieved a database row as a hashref, like so:

my $hashref = {};
my $class = Fieldmapper::class_for_hint('bre');
my $bre = $class->from_bare_hash($hashref);

We also modify the Fieldmapper's properties method to sort the array of
field names it returns by position.  This makes the return value a lot
more useful for on the fly object construction and other fancy tricks.

Signed-off-by: Jason Stephenson <jstephenson@mvlc.org>