Change public interface to return boxed dynamic error instead of String.

src/parser/document.rs

@@ -28,7 +28,7 @@ use crate::types::Object;
 ///
 /// This is the main entry point for Organic. It will parse the full contents of the input string as an org-mode document.
 #[allow(dead_code)]
-pub fn parse<'s>(input: &'s str) -> Result<Document<'s>, String> {
+pub fn parse<'s>(input: &'s str) -> Result<Document<'s>, Box<dyn std::error::Error>> {
     parse_with_settings(input, &GlobalSettings::default())
 }
 
@@ -41,7 +41,7 @@ pub fn parse<'s>(input: &'s str) -> Result<Document<'s>, String> {
 pub fn parse_with_settings<'g, 's>(
     input: &'s str,
     global_settings: &'g GlobalSettings<'g, 's>,
-) -> Result<Document<'s>, String> {
+) -> Result<Document<'s>, Box<dyn std::error::Error>> {
     let initial_context = ContextElement::document_context();
     let initial_context = Context::new(global_settings, List::new(&initial_context));
     let wrapped_input = OrgSource::new(input);
@@ -49,7 +49,7 @@ pub fn parse_with_settings<'g, 's>(
         all_consuming(parser_with_context!(document_org_source)(&initial_context))(wrapped_input)
             .map_err(|err| err.to_string())
             .map(|(_remaining, parsed_document)| parsed_document);
-    ret
+    Ok(ret?)
 }
 
 /// Parse a full org-mode document.