| (lists-to-xml list?) -> string? | 
convert lists to xml, the list should obey below rules.
1. First node of list should be a string? or symbol? It represent node name.
2. All the pairs represent node’s attributes.
| '("H1" ("attr1" . "1") ("attr2" . "2")) -> <H1 "attr1"="1" "attr2"="2"/> | 
3. If have children, string/symbol represent its value, or, the lists represents its children.
        Node’s children should either string? or symbol? or lists?, only one of these three types.
| '("H1" "haha") -> <H1>haha</H1> | 
|  | 
| '("H1" ("H2" "haha")) -> | 
|  | 
| <H1> | 
| <H2> | 
| haha | 
| </H2> | 
| </H1> | 
| (lists-to-compact_xml list?) -> string? | 
remove all the format characters.
| '("H1" ("H2" "haha")) -> <H1><H2>haha</H2></H1> |