Add hyperlinks to fix `cargo doc` warn (#931)

helix-core/src/graphemes.rs

@@ -1,6 +1,6 @@
 //! Utility functions to traverse the unicode graphemes of a `Rope`'s text contents.
 //!
-//! Based on https://github.com/cessen/led/blob/c4fa72405f510b7fd16052f90a598c429b3104a6/src/graphemes.rs
+//! Based on <https://github.com/cessen/led/blob/c4fa72405f510b7fd16052f90a598c429b3104a6/src/graphemes.rs>
 use ropey::{iter::Chunks, str_utils::byte_to_char_idx, RopeSlice};
 use unicode_segmentation::{GraphemeCursor, GraphemeIncomplete};
 use unicode_width::UnicodeWidthStr;

helix-core/src/history.rs

@@ -40,7 +40,7 @@ use std::time::{Duration, Instant};
 ///  * Because delete transactions currently don't store the text that they
 ///    delete, we also store an inversion of the transaction.
 ///
-/// Using time to navigate the history: https://github.com/helix-editor/helix/pull/194
+/// Using time to navigate the history: <https://github.com/helix-editor/helix/pull/194>
 #[derive(Debug)]
 pub struct History {
     revisions: Vec<Revision>,