[graphviz] add attribute HtmlLabel
Use 97 as default size when creating hash tables

- avoid putting too much pressure on OCaml's gc
- Fixes #14
Merge pull request #15 from backtracking/size-hash-tables

Use 97 as default size when creating hash tables
slides meeting OUPS July 2014
slides meeting OUPS July 2014 (last minute edit)
Minimal cutset algorithm.