Add module doc comments

src/dijkstra.rs

@@ -1,3 +1,6 @@
+//! Implements Dijkstra's algorithm for shortest path, to find an
+//! optimal and readable diff between two ASTs.
+
 use std::cmp::{min, Ordering, Reverse};
 use std::collections::BinaryHeap;
 use std::hash::{Hash, Hasher};

src/intervals.rs

@@ -1,3 +1,5 @@
+//! A range between ordered values.
+
 /// An interval that is inclusive of `from` but exclusive of `to`.
 ///
 /// This is a an alternative to `Range`, which has some API warts:

src/lines.rs

@@ -1,3 +1,5 @@
+//! Manipulate lines of text and groups of lines.
+
 use crate::intervals::Interval;
 use crate::positions::SingleLineSpan;
 use crate::syntax::{aligned_lines, MatchKind, MatchedPos};

src/parse.rs

@@ -1,3 +1,5 @@
+//! Lexes source code and parses delimiters according to `syntax.toml`.
+
 use crate::lines::NewlinePositions;
 use crate::positions::SingleLineSpan;
 use crate::syntax::Syntax;

src/positions.rs

@@ -1,3 +1,5 @@
+//! Represents positions within a string.
+
 use crate::lines::LineNumber;
 
 /// A range within a single line of a string.

src/style.rs

@@ -1,3 +1,5 @@
+//! Apply colours and styling to strings.
+
 use crate::lines::LineNumber;
 use crate::positions::SingleLineSpan;
 use crate::syntax::{MatchKind, MatchedPos};

src/syntax.rs

@@ -1,3 +1,5 @@
+//! Syntax tree definitions with change metadata.
+
 #![allow(clippy::mutable_key_type)] // Hash for Syntax doesn't use mutable fields.
 
 use itertools::{EitherOrBoth, Itertools};