Add `MERGE` Support

• Add MERGE support: https://docs.snowflake.com/en/sql-reference/sql/merge
  • Limit Sequel gem to >= v5.58.0 to support this functionality.

Add support for `EXPLAIN`

• Add support for EXPLAIN.

Switch to MIT License

• Switch to MIT license for open source purposes
• Add GitHub Actions to run CI via GitHub runners and push to RubyGems on merge

Initial Release

• Handle parsing Snowflake values for the following types:
  • Numeric data types
  • String data types
  • Booleans
  • Dates
• Support insertion of multiple rows using the VALUES syntax.
• Support creating tables with String columns with maximum varchar size (16777216).