Option to change just the metavar prefix. Fixes #13.
working on histogram for all types.
changed schema according to #12.
0.4.0
modified readme to match latest schema schema changes
added warning about schema change.
Revert "histogram for any data type". This was not a very useful idea. It makes more sense
to treat categories as their own data type.

This reverts commit 21436f080131276b51998e827960ebed6977d7a5.
schema is now versioned. fixed some tests.
0.5.0
replace default prefix $ with #, make flat:true default.
changed README, prefix not added to __schema options
0.5.1
fixed some doc bugs
0.5.2
changed description of package.