Allow hypergraph output to be in plain text, gzip, or bzip2.

The output-search-graph-hypergraph flag now takes two params:

* The first param must be "none", "gzip", or "bzip2"
* The second param is the hypergraph directory,
  which must already exist
Work on compression and defaults for outputting hypergraphs.
Ensure directory exists for outputting hypergraphs