RBFS and romania are working.
Move graph/tiles to tiles
[romania] Add func (c City) String() string
[romania] Add ExampleNew()
[graph] Remove needless NewProblem.
[graph] gofmt
Use github.com/glenn-brown/builtin for cost.
[tiles] track cost changes.
[ch4/test/sdldoc.go] Example from SDL docs now compiles.
Add eg.c from sdldoc.pdf.
[sdlgears.go] Initial version.  Does not compile.
Progress on ch4/p11.