Added Snowflake and RedShift support

Added Redshift and Snowflake support

Added more tests, test generation functionality, and docs

Merge pull request #4 from kgmcquate/develop

Added more tests, test generation functionality, and docs

Easier test generation

Generate all types of tests using 1 macro:
testgen.get_test_suggestions(ref('mymodel'))

All tests working on duckdb and postgres.

v0.1.0

3 test generator macros are working with DuckDB:

• accepted_values
• range
• unique

Basic integration tests are written and automated.