add more response types, form binding support, tls support

[KARTIKrocks]

Added

• request — BindForm[T] and BindFormWithConfig[T] for application/x-www-form-urlencoded body binding with struct tags (form:"name")
• request — BindMultipart[T] and BindMultipartWithConfig[T] for multipart/form-data body binding
• request — FormFile(r, field) returns a single uploaded file header; FormFiles(r) returns all uploaded files
• request — Bind[T] now auto-detects content type: JSON, form, and multipart are dispatched automatically; unknown types return 415
• request — BindJSON[T] and BindJSONWithConfig[T] for explicit JSON binding with content-type enforcement
• request — MaxMultipartMemory field on Config (defaults to 32 MB) controls multipart memory threshold
• request — form struct tag supported in field name resolution for validation errors (checked before json tag)
• server — WithTLS(certFile, keyFile) option for HTTPS support
• server — Addr() method returns the listener address after the server starts
• response — XML(w, statusCode, data) writes XML responses with <?xml?> header
• response — IndentedJSON(w, statusCode, data) writes pretty-printed JSON
• response — PureJSON(w, statusCode, data) writes JSON without HTML escaping of <, >, &
• response — JSONP(w, r, statusCode, data) writes JSONP responses (reads ?callback= query param)
• response — Reader(w, statusCode, contentType, contentLength, reader) streams from io.Reader