message: [style] remove snake case from style guide
diff: - Names shall not give any idea of type, such as is done with System Hungarian notation.
  - Case
  - C preprocessor symbols should be all uppercase.
  - - All OpenThread names in the C language shall be in *snake case*.
  - - All OpenThread class, namespace, structure, method, function, enumeration, and type names in the C++ language shall be in *upper camel case*. Exception: the top level OpenThread namespace 'ot'.
  + - All OpenThread class, namespace, structure, method, function, enumeration, and type names in the C/C++ language shall be in *upper camel case*. Exception: the top level OpenThread namespace 'ot'.
  - All OpenThread instantiated names of instances of classes, namespaces, structures, methods, functions, enumerations, and types as well as method and function parameters in the C++ language shall be in *lower camel case*.
  - Symbol Qualification
  - All OpenThread C public data types and free functions should have `ot` prepended to their name.
  ## Standards
  -- OpenThread uses and enfores both Python 2 and Python 3. Support for Python 2 is a result of the fact that some current Linux distributions and Macs are still using 2.x as default.
  +- OpenThread uses and enforces both Python 2 and Python 3. Support for Python 2 is a result of the fact that some current Linux distributions and Macs are still using 2.x as default.
  ## Conventions and Best Practices
  