minor coding style fixes and micro optimizations in ngx.md5, ngx.encode_base64, and ngx.decode_base64.
bugfix: temporary memory leaks might happen when using ngx.escape_uri, ngx.unescape_uri, ngx.quote_sql_str, ngx.decode_base64, and ngx.encode_base64 in tight Lua loops because we allocated memory in nginx's request memory pool for these methods.
optimize: ngx.escape_uri now runs faster when the input string contains no special chars to be escaped.