Use single letter receiver labels

Given the locality of the use with the definition all the methods, more
than a single character seems unnecessary. This is in line with the
standard library convention for receiver naming.
Reduce stutter in labels

TODO There is more room for simplifying labels, but at the moment labels
are standing in for doc comments. When these are fleshed out another
sweep can be done.
Add LICENSE notices
Merge pull request #10 from gonum/house-keeping

Changes to reduce documentation clutter and add LICENSE details