Find closing parenthesis position, given opener's

  * Walks through each character
  * If it's "(", it adds one to the counter
  * If it's ")", it subtracts one from the counter
  * If the counter hits zero, returns the current position
  * Skips all other letters
Merge pull request #2 from mknudsen01/bracket-validator

Find closing parenthesis position, given opener's