Extended ordering methods.

Deprecate old methods.
Introduce:
 * up() ....... replaces move_up()
 * down() ..... replaces move_down()
 * down() ..... replaces move_down()
 * swap() ..... swap position with another object
 * to() ....... move object to arbitrary position
 * above() .... move object above reference object
 * below() .... move object below a reference object
 * top() ...... move object to top of stack
 * bottom() ... move object to bottom of stack
Add tests for all new methods.
Make assertions more specific by including the resulting order value.
Clean up trailing white spaces.
Add documentation describing each method.
Merge pull request #9 from fladi/move_freely

Extended ordering methods.