add docs for to_s and encoding
add docs for to_s and encoding

xml4r/libxml-ruby,sferik/libxml-ruby,xml4r/libxml-ruby,sferik/libxml-ruby,increments/libxml-ruby,increments/libxml-ruby,sferik/libxml-ruby,sferik/libxml-ruby,xml4r/libxml-ruby,sferik/libxml-ruby,sferik/libxml-ruby,increments/libxml-ruby