Add some travis stuff for dep graphs
Add dpdgraph-0.4alpha

From https://anne.pacalet.fr/dev/dpdgraph/dpdgraph-0.4alpha.tgz
Also graphviz
Make dpd_graphs
Apply Yves' patch
Fix name changes
Strip trailing spaces
Various fixes for HoTT
type_of_constant_type seems unneeded
Add hoqthmdep
Fix hoqthmdep
Allow specifying a graph name
Add some targets to make dependency graphs
Don't error on empty Coq files