`Relation#create_get` and `#create_scan` pass columns as options.

Particularly the keys are qualifier names, and the values are either
qualifiers or arrays of qualifiers if more than one for the schema is
desired.

The row bounds of scans have also been absorbed into this options
hash, under the keys `:start` and `:stop`.  If the user needs
qualifier schemas with these names (or shortly, `:families` or
`:filter`), they may still pass them as string keys to have them be
interpreted as schema names.
`Relation#create_scan` understands families and scan filters.

A single family can be passed directly by name with the `:family`
option.  `:families` instead takes a list.

`:filter` can take either a filter string (parsed with HBase's
`ParseFilter`), or a direct filter object.  `#create_scan_filter`
encapsulates the filter parser, allowing the user to parse once and
reuse a filter many times.