Test JSON-value character getters and add copyrights

This release

1. Adds passing tests for three private string_t type-bound procedures supporting the public generic binding get_json_value:
   • get_character 🔠
   • get_character_with_character_key 🔑
   • get_string_with_character_key 🧶
2. Adds missing copyright headers to all files in two subdirectories:
   • example/ and 🚗
   • test/. ☑️

What's Changed

• Feature/Chore: new get_json_value getters / add copyrights by @rouson in #10

Full Changelog: 1.1.0...1.1.1