Modernize (#149)* add .clang-format for automated code formatting* automatic code formatting* move config.mk below all target to allow custom non-default build targets* add license to the top of the file* use correct header file guards syntax* convert to single-header, header-only library* update makefile to use jsmn as a header-only library* update readme* add changed from PR#143* fix clang warnings* add changes from PR#142* add consts as per PR#134

Most well-known stable version that made jsmn popular