Circle - invalid r value

[rhauck]

No description provided.

[betravis]

"Invalid values" represent unsupported value types (for r, values like "auto" or "#ffffff"), rather than values that are of the correct type but do not meet other spec requirements (such as being nonnegative).

For the most part, specific spec rules, such as being non-negative, are tested in pull request #2.

[betravis]

See also issues #127, #126, #120, #118, #117, #115, #87, #86, #71, #70, #69, #66, #42, #41, #31, #30, #29, #27.