v0.3.4

New features:

• allow map_*_channels to broadcast singletons (e.g. map_value_channel(foo, \(x) "bar"))
• vectorized format() and vec_proxy_equal() functions improve performance
• allow lossy casts with cfactors (when cfactors are cast to fewer codes, but no values are at that level)

Bug fixes:

• rework some cfactor ptype2 and casting to match factor behavior better (e.g. lossy casts)
• add more exhaustive tests for cfactors