OpenBrush v0.2.0-rc1

• Added ability to store the definition of traits, methods and etc in the temporary metadata file.
• Added brush::impl_trait macro which generates external implementation based on external trait defined via ink::trait_definition. It uses function with according naming from internal trait.
• Added brush::contract macro which consumes impl_trait macro before ink codegen.
• Added brush::trait_definition to hide reflaction functionality.
• Removed underscore from all public methods inside of internal trait.
• Removed Erc*Internal traits. All methods from them moved to accord external trait.
• Simplified public functions to not return results with errors. Now all contracts will assert if some inner check can't be passed.
• Moved unit tests to separate folders.