Pipgrip

* :sparkles: Add detailed json tree (--json --tree)

* :loud_sound: Add debug for failed wheel fname extraction

* :sparkles: Add --tree-ascii, --tree-json, --tree-json-exact options

* :recycle: Refactor --tree-json-exact eliminating one recursive function

:checkered_flag: Match fetched wheel filenames using lower case (30)

:bug: Avoid parsing mixology Constraint back to pip string (28)

* support `--install-user` argument (syn: `--user`)

* :recycle: Use --user only to stay close to pip interface

* :pencil: Bump pipgrip deptree to 0.4.0 in README