Restructure appveyor.yml
Restructure appveyor.yml

Split the script into three parts, instead of one large block. Because
of the block structure, errors didn't show up because only the last
command was evaluated when determining whether the build was successful.
These errors should now be visible.

ellson/graphviz,ellson/graphviz,ellson/graphviz,ellson/graphviz,ellson/graphviz,ellson/graphviz,ellson/graphviz,ellson/graphviz,ellson/graphviz,ellson/graphviz,ellson/graphviz