0.2

Changes:

• (api change) add SharedString and use it instead of std::string_view, it make lifetime management much easier
• (api change) remove getCacheControl and setCacheControl from HttpRequestHeaders
• (api change) change paramter type from const HttpServerRequestHandlerIterator& to HttpServerRequestHandlerIterator in http request handler
• (api change) require types under cpv::extensions::http_context_parameters when registering http request handler with parameters
• add json serializer and deserializer
• add form serializer and deserializer
• add static file handler
  • support pre-compressed gzip (detect original-filename.gz)
  • support bytes range
  • support return 304 not modified when If-Modified-Since matched
• add benchmark tools