Use adjectival forms for modifiers that add shapes around a base

[MDLC01]

#34 was closed by changing .circle to .o, which makes sense because circling mathematical operator is quite common. As I expressed in #62 (comment), I believe .o should be kept for circling mathematical symbols only. For now, no circled symbol in Codex is not a mathematical operator. However, other modifiers that cause the base symbol to appear inside a geometric shape I propose to use an adjectival variant instead. This would change .square to .squared, .triangle to .triangled, and an hypothetical .circle for geometric shapes to .circled.