Add bindParameterIndex for working with named bound parameters

Add Database.SQLite3.Direct support for querying the index of a named
parameter in a statement.

Named parameters (e.g. 'SELECT :foo') allow for some convenient forms
of developing SQL queries that are harder to write and maintain with
positional arguments.
Add bindNamed convenience function
Merge pull request #44 from nurpax/named-params

Add bindParameterIndex for working with named bound parameters