added linear difference, weighted linear difference, and exponential difference as methods for choosing
added functions to call to choose engineers based on linear difference, weighted linear difference, and exponential difference
fixed issues with weighted linear and exponential choices where it was penalizing engineers by the preference weights if they met the managers preference on the dot. Also wrote some checks in the test to display how they are different. These methods need to be tested I will work on that now
Merge branch 'master' into egan
Need to get egan up to date before submitting pull request
Merge pull request #4 from AEgan/egan

linear / exp / weighted changes to manager choice