BST and Mergesort Code for Sept 14th#2

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ulbanata wants to merge 2 commits intomasterfrom

Commits on Sep 14, 2014

Added mergesort, page 271. Includes a single aux_arr for in-place sorting
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Added Binary Search Tree code for page 398. Can only add and get key/value pairs right now. No balancing or removing.
ulbanata
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