Summary of changes

• [bugfix] http server plugin example fixed
• [feature] go mod tidy
• [upgrade] switch to go modules
• [feature] godoc for http plugin packages added
• [feature] Return all headers from proxy response
• [feature] add to mux router funk clientIP
• [upgrade] log improved
• [bugfix] handler namespace fixed
• [feature] http handler injection via plugin added
• [feature] noop param extractor exported
• [feature] code line of sight improved
• [feature] use latest golang version 1.13.1
• [feature] multilevel selection of parameters for sequential pipes
• [feature] Push KrakenD User-Agent only if not overriding forwarded Header