Mathml parser

This implements a parser for the MathML spec https://www.w3.org/TR/2003/REC-MathML2-20031021/chapter4.html At the moment only content markup is implemented

Usage example

rust use mathml::parse_document; let test = "<math xmlns=\"http://www.w3.org/1998/Math/MathML\"> <apply> <plus/> <ci> x </ci> <ci> y </ci> </apply></math>"; let res = parse_document(test).unwrap(); let exp = Root(vec![Apply(vec![ Op(BuiltinOp::plus), Ci(vec![Text("x".to_owned())]), Ci(vec![Text("y".to_owned())]), ])]); assert_eq!(res, exp);