Create and print xml trees

`val tag_err : string`
`val tag_file : string`
`val tag_in_calls : string`
`val tag_line : string`
`val tag_loc : string`
`val tag_name : string`
`val tag_name_id : string`
`val tag_out_calls : string`
`val tag_proof_coverage : string`
`val tag_proof_trace : string`
`val tag_rank : string`
`val tag_signature : string`
`val tag_specs : string`
`val tag_symop : string`
`val tag_time : string`
`val tag_to : string`
`val tag_top : string`
`val tag_weight : string`