Add variants for Persian layout

Added the following variants for Persian:

• Persian (with U+06C0) - ir(pes_u6c0)

  • Same as the standard layout, but with an extra symbol: U+06C0 assigned to AltGr + G

• Persian (with U+06C0 and Persian keypad) - ir(pes_u6c0_keypad)

  • Same as Persian (with Persian keypad), but with an extra symbol: U+06C0 assigned to AltGr + G

• Persian (Windows) - ir(pes_winkeys)

  • Based on the Persian layout of Microsoft Windows, with extra level-3 symbols for compatibility with the standard layout.
  • Fixes #367

Let me know if anything seems wrong or should be changed.