refactor: misc

[reiniiriarios]

• when strcmp already exists, compiler throws error that int16_t is not int
• add strncasecmp
• split i2c and user commands into own functions
• simplify command type filtering logic
• refactor command struct to class
  • this makes more sense as this code doesn't need to be visible to end-user
  • if keeping this, my recommendation is to make properties private that can be
• fix i2c command/args length issue
  • if my understanding is correct, the end result of removeSpaces is that, in the case of I2CWFFFFFF, the cmdLength will be 10 and argsLength 0??
• simplify error setting
  • the error_t struct needs access to the PROGMEM strings
  • alternative approach: move set() fn outside of error_t struct
  • alternative approach: refactor error_t to Error class, implemented in cpp file instead