more strict create() and rename()

* add schema_exists(), table_exists()
* validate params in create(), rename()
add quote_name(). using it, fv will be able to use source tables with special chars in their names, or names which are keywords
refined set_definition()
trivial tests (draft)
Merge pull request #6 from santec/master

more checks on create() rename() set_definition() params + trivial tests