Fixing spec of spline calibration matrices
Minor code clean up
No longer exporting abstract types

These can be extended by downstream packages using the `import` command:
http://docs.julialang.org/en/release-0.3/manual/modules/
Fixed error in natural spline calibration matrices

The OG document states that b = (0, s_2 - s_1, ...., s_{n-1} -
s_{n-2}}). However, it should be 6 * (0, s_2 - s_1, ...., s_{n-1} -
s_{n-2}}).

Also added debug info
Taking the multiplier out the front of vector
Removing debug info
Adding test cases for natural cubic spline
Fixed multiplier on array
Added more NCS test cases