# =-=-=-= DAY 98 [Easy] =-=-=-=
#
# Given a 2D board of characters and a word, find if the word exists in the grid.
# 
# The word can be constructed from letters of sequentially adjacent cell, where
# "adjacent" cells are those horizontally or vertically neighboring. The same
# letter cell may not be used more than once.
# 
# For example, given the following board:
# 
# [
#   ['A','B','C','E'],
#   ['S','F','C','S'],
#   ['A','D','E','E']
# ]
