This fixes the capitalisation of Gonum where it refers to the project rather
than the GitHub organisation or repository. The text of CONTRIBUTORS also
is fixed to reflect the reality that contributors may have contributed to
other repositories within the project.
Currently variant line types do not work the same way as they would with
a slice of edges because access to a []graph.Edge also allows the
elements of that slice can be type asserted to richer types like
graph.Line or graph.WeightedEdge for example. This cannot be done with
the API as is stands with the iterator-holding edge being down graded
from one of the richer types.
The problem can be avoided by either making graph.WeightedLines also
satisfy graph.Lines (same for edges), or by down-typing the edges in the
non-weighted edge return methods for the graph implemetations.
