Compile do_circ
Add writeTxtAll, toString(int)

writeTxtAll() writes the whole text description, including unused edges, to a
file.  toString now has a parameter (default 1) which is the lowest colour to
describe in the output.  setting it to 0 shows unused edge.
Fix checkpointing on last step
Fix compilation of do_circ
Fix start parameter for Cycle
Add lowest parameter to Cycle step

If true, the Cycle step will only attempt to place a cycle on the
vertex which has the lowest index.
Fix lowest parameter
Add do_twofactor program
Merge branch 'master' of github.com:WPettersson/graphlib