Feat(compute): Write powers of fraction

mapytex/calculus/API/__init__.py

@@ -32,6 +32,15 @@ Generate and compute like a student!
 4 / 2 + 3 / 2
 (4 + 3) / 2
 7 / 2
+>>> e = Expression.from_str("(2/3)^4")
+>>> e_simplified = e.simplify()
+>>> print(e_simplified)
+16 / 81
+>>> for s in e_simplified.explain():
+...    print(s)
+(2 / 3)^4
+2^4 / 3^4
+16 / 81
 
 """