Added 'random_element' operator.

The gmpy2 digits( ) function is a much faster way to convert numbers to bases 2 through 62.

Added support for using yafu for factoring.

Added 'aliquot_limit' operator.

Added support for user configuration: 'set_config', 'get_config', 'delete_config' and 'dump_config'.

Added the 'mothers_day', 'fathers_day' and 'advent' operators.

Added the 'molar_gas_constant', 'aliquot_limit' and 'distance' operators (the old 'distance' operator is now called 'geo_distance').

Added unit tests for converting units, and made a few fixes accordingly.

Verbose mode for factoring gets turned on with -D.

Oops, there were two operators named 'distance'. 'distance' now refers to the physics operator and the geography operator is now named 'geo_distance'.

The 'acceleration' operator has been implemented.

The derived Planck units are now calculated, instead of hard-coded.

Block Hole operators: 'black_hole_entropy', 'black_hole_lifetime', 'black_hole_luminosity', 'black_hole_mass', 'black_hole_radius' (was 'schwarzchild_radius'), 'black_hole_surface_area', 'black_hole_surface_gravity', black_hole_temperature'

...and the usual bug fixes.