* refactor(form_mapping.go): mapping multipart request
* add checkers for a types to match with the setter interface
* form_mapping.go: rename method name on setter interface, add comments
* fix style of comments
* refactor(form_mapping.go): mapping ptr, struct and map
* fix#1672 correct work with ptr - not create value if field is not set
* avoid allocations on strings.Split() - change to strings.Index()
* fix#610 tag value "-" is mean ignoring field
* struct fields mapped like json.Unmarshal
* map fields mapped like json.Unmarshal
* fix after @thinkerou review
* fix Context.Next() - recheck len of handlers every iteration
* add tests when Context.reset() can be called inside of handler
TestEngineHandleContext
TestContextResetInHandler
TestRouterStaticFSFileNotFound
* Context.Next() - format to while style
Dmitry Kutakov