Improve release script

[plbstl]

This PR updates the release script to be slightly more robust, and updates related documentation.

The new implementation:

• Improves debug messages
• Retrieves semver tag from a commit with duplicate tags (e.g. v2, v2.1.2)
• Retrieves the latest release tag from current branch only
• Pushes the new release tag along with necessary commits to remote
• Works with only annotated tags
• Updates the separate major tag to point to the new release
• Terminates the script when a command fails
• Boldens the colored text in terminal
• Uses full flags for commands, where applicable
• Auto-detects major releases
• Creates a releases/v# branch for the previous major version, when creating a major release