Alpha release of YW 1.0 with builtin Graphviz library

This is the first release of YW that can produce SVG images of workflow graphs using a statically linked, minimal Graphviz library. A separate Graphviz installation is no longer required on the user's computer. However, YW can still output DOT format for use with a full-featured Graphviz installation, e.g. if other graphics formats are needed.