Complete code review

[globusharris]

Review all code. Verify:

• correctness

• complete commenting

• complete citations

• readability

• mechanism-bootstrap

• mechanism-exponential

• mechanism-gaussian

• mechanism-laplace

• mechanism-objective

• mechanism

• statistic-covariace

• statistic-glm

• statistic-heavyhitters

• statistic-histogram

• statistic-mean

• statistic-tree

• statistic-variance

• utilities

• testing files