Phs/scan families and filters

`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.

`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 any of the other new options), they may still pass them as string keys to have them be interpreted as schema names.