Always convert CRLF into LF-only line endings.

CRLF lineendings will happen on Windows,
but they shouldn't matter for Markdown content.

pulldown-cmark will parse them _nearly_ the same.
`<!-- toc -->\r\n` will actually be 2 HTML elements:
the `<!-- toc -->` part and a `\n` part,
whereas `<!-- toc -->\n` will be just one: `<!-- toc -->\n`.
That throws off our marker parser because we're looking for the latter only.

So by stripping our the CR (`\r`) we don't need to special-case anything.
The rendering will be the same.

Closes #35

src/lib.rs

@@ -149,10 +149,12 @@ fn add_toc(content: &str, cfg: &Config) -> Result<String> {
     opts.insert(Options::ENABLE_TASKLISTS);
 
     let mark: Vec<Event> = Parser::new(&cfg.marker).collect();
+    log::trace!("Marker: {:?}", mark);
     let mut mark_start = None;
     let mut mark_end = 0..0;
     let mut mark_loc = 0;
 
+    let content = content.replace("\r\n", "\n");
     for (e, span) in Parser::new_ext(&content, opts).into_offset_iter() {
         log::trace!("Event: {:?} (span: {:?})", e, span);
         if !toc_found {

tests/it.rs

@@ -164,3 +164,8 @@ fn empty_document() {
     // Empty documents should not fail
     assert_toc!("empty_document");
 }
+
+#[test]
+fn crlf() {
+    assert_toc!("crlf");
+}