changing license to MIT and removing GPL license headers

[ParticularlyPythonicBS]

Summary by CodeRabbit

• Chores
  • Project license changed from GNU GPLv2 to MIT (copyright 2015–2025); legacy GPL license file removed and new LICENSE added; packaging metadata updated to reflect MIT.
  • .gitignore adjusted to track the new license filename.
• Documentation
  • Removed or simplified legacy file header/license comments and minor docstring wording clarifications across several modules.

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