Adds comment feature.

This release adds the ability to comment lines in the Godeps file, like so:

github.com/pote/johnny-deps-testing-package   v5.0
#github.com/VividCortex/ewma                  v1.0
# This line is a comment.
                          # this is an oddly-placed comment

It should be noted thought that in the interest of simplicity only lines that begin with a # are comments, so therefore comments like the one below are not supported.

github.com/pote/johnny-deps-testing-package v5.0    # This is an invalid comment.