Function parse 

pub fn parse(text: &str) -> BTreeMap<String, BTreeSet<String>>

Parse an ASCII DAG. Extract edge information. Return a map from names to their parents.

The direction of the graph is automatically detected. If | is used, then roots are at the bottom, heads are at the top side. Otherwise, - can be used, and roots are at the left, heads are at the right. | and - cannot be used together.

Example:

use drawdag::parse;

let edges = parse(
    r#"
            E
             \
    C----B----A
       /
     D-
"#,
);
let expected =
    "{\"A\": {\"B\", \"E\"}, \"B\": {\"C\", \"D\"}, \"C\": {}, \"D\": {}, \"E\": {}}";
assert_eq!(format!("{:?}", edges), expected);

let edges = parse(
    r#"
  A
 /|
| B
E |
  |\
  C D
"#,
);
assert_eq!(format!("{:?}", edges), expected);