completion support for non default schema

[aokiji]

As seen in #99 and #121 there is lack of support for completion when working with other schemas/databases other than the default schema/database. So this in the initial effort to fix this issue bringing support for:

• table completion when given the schema
• table description for table in any schema
• column completion when given table in any schema
• column completion for tables in any schema referenced in the join clause

Test were added so that the new features/changes are covered

[mattn]

Looks good.