Write a function named reverse_complement that accepts a single string parameter representing a sequence of DNA bases and returns its reverse complement. The reverse complement is obtained by changing each base (letter) to its complement and reversing the sequence. A and T are each others' complements; G and C are complements.

Given the string "A", you would return "T" because T is the complement of A. Given "AG", you would return "CT" because T is the complement of A, C is the complement of G, and reversing "TC" produces "CT".

You may assume that the input string contains only capital A, C, G, and T characters.