Implement Double for ALINE

[chrislit]

See: https://www.aclweb.org/anthology/A00-2038

Double-articulations, like /w/, get special handling according to the paper. This wasn't implemented in Abydos 0.4.0.

[chrislit]

Example where there should be difference:

168 self.assertEqual( 169 self.cmp.alignment('wat', 'vas'), 170 [(40.0, 'w ‖ a t ‖', 'v ‖ a s ‖')], 171 )