Schemachange

Added
- Added a Snowflake query tag to all snowchange queries. If the query is issued by the tool the tag will be "snowchange .." (e.g. "snowchange 2.7.0") and if the query is part of a change script the tag will be "snowchange ..;<script name>" (e.g. "snowchange 2.7.0;V1.1.1__initial_database_objects.sql")

Added
- Added a new optional parameter `-d` or `--snowflake-database` to specify the default database to use (which can always be overridden in an individual change script)
- Added a new optional parameter `--create-change-history-table` to create the change history table if it does not exist

Changed
- The default mode of operation now is to not create the change history table if it doesn't exist. Instead, now if the history table doesn't exist the tool will fail by default.
- Added a check to see if the change history table exists before trying to create it, which is now also dependent upon the `--create-change-history-table` command line argument.
- Cleaned up command line argument descriptions

Removed
- Removed the ability for snowchange to create the database for the change history table. snowchange now requires the database to be created ahead of time.

Added
- Support for encrypted key pair authentication

Added
- PyPI package support so that snowchange can be installed through pip
- Dockerfile for building Docker images

Changed
- Allow for .SQL file extensions (common in Windows environments) in addition to .sql extensions

Added
- Support for "repeatable" scripts such as stored procedures, functions etc

Added
- Support for variables in change scripts (following a Jinja expression syntax)! See the [README](README.md) for more details.
- A new optional parameter `--vars` which accepts a JSON formatted string of variables and values (e.g. `{"variable1": "value1", "variable2": "value2"}`)

Changed
- Add the Snowflake account name to the script output to provide more log context

Removed
- Removed the deprecated `--snowflake-region` parameter. Instead, use the `-a` or `--snowflake-account` account parameter. See [Usage Notes for the account Parameter (for the connect Method)](https://docs.snowflake.com/en/user-guide/python-connector-api.html#label-account-format-info) for more details on how to structure the account name.