Add a document about the "region-type" property
Add tests on the "region-type" property
Treat "region-type" as a non-UI property name
Define the default "region-type"
Support region types to #select
Support "region-type" for "select"
Support region types to #select_pair
Support "region-type" for "select-a"/"select-i"
Refactor - Simplify RHS of pattern-based objects

The old code passes flags via RHS.  It makes things complicated if flags
contain special characters such as "\<C-v>".
Refactor - Simplify RHS of function-based objects
Merge branch 'support-region-type'

Close gh-24.
Add release notes on 0.6.0
Bump up version to 0.6.0
Merge branch 'prepare-for-0.6.0'