Remove backward compatibility aliases and update to standalone functions

[eman]

This maintenance release cleanup removes deprecated backward compatibility layers:

Changes

Constants Module

• ✅ Removed backward compatibility aliases (13 aliases)
• ✅ Updated examples to use enum directly

CLI Module

• ✅ Removed backward compatibility wrapper module
• ✅ Updated entry point to use nwp500.cli.__main__:run directly

Encoding Functions

• ✅ Updated examples to use standalone functions:
  • build_tou_period() instead of NavienAPIClient.build_tou_period()
  • encode_price() / decode_price() instead of NavienAPIClient.*
  • encode_week_bitfield() / decode_week_bitfield() instead of NavienAPIClient.*

Documentation

• ✅ Updated time_of_use.rst to reference standalone functions
• ✅ Updated reservations.rst to reference standalone functions
• ✅ Updated constants.rst to remove backward compatibility section
• ✅ Fixed broken relative links in README.rst
• ✅ Added Read the Docs and GitHub links to README.rst header

Examples Fixed

• ✅ anti_legionella_example.py
• ✅ exception_handling_example.py (deprecated method name)
• ✅ tou_openei_example.py
• ✅ tou_schedule_example.py

Validation

• ✅ Linting: All checks passed
• ✅ Type checking: No issues found
• ✅ No remaining CMD_* usage in codebase
• ✅ No remaining NavienAPIClient.* static method usage in examples/docs

Breaking Changes

None - all deprecated APIs were already replaced with new ones in previous releases. This just removes the old compatibility layers.