Matrices

Started work on the matrix library.
Constructor

Written the preliminary matrix validation check.
Tests and Dimensions

Wrote tests for the constructor, wrote the dimension functions, wrote
tests for the dimension functions.
Addition and Tests

Wrote the addition function, wrote some more tests.
Subtraction, Scaling, and Callbacks

Added subtraction by scaling $that by -1. Added scaling by applying a
closure to all elements. Added that function. Tests for days.
Merge pull request #4 from tomalom/dev-master

Adding in the matrix work so far.