feat: export an esm module

[iambumblehead]

additionally export an esm module file

an indirect solution to iambumblehead/esmock#312

cc Filipoliko

I use a similar formulae to this with form-urlencoded and it is used by many people for both cjs and esm.

[iambumblehead]

need to replace the require/import calls...

[iambumblehead]

using this patch, the related sample test passes with this branch

diff --git a/repro.test.mjs b/repro.test.mjs
index d32fe0c..b5ca1f1 100644
--- a/repro.test.mjs
+++ b/repro.test.mjs
@@ -12,7 +12,9 @@ test('parseChangelog', async () => {
             read: mock.fn(() => content),
         },
         'line-reader': { // This does not get mocked in `changelog-parser` module
-            readLine: mock.fn(() => content),
+            eachLine: async (fpath, cb, eol) => {
+              cb('content')
+            },
         }
     });
 
@@ -20,5 +22,8 @@ test('parseChangelog', async () => {
         filePath: 'fake',
     });
 
-    assert.equal(changelog, content);
+    assert.deepEqual(changelog, {
+       versions: [],
+       description: content
+    });
 });

tbh I'm not sure if the patch to changelog-parser is needed. part of the issue at the esmock ticket is the line-reader's "readLine" is mocked at 'changelog-parser' but changelog-parser never imports readLine so of course nothing happens.

@Filipoliko try mocking eachLine rather than readLine I would try myself but unfortunately have to take care of something right now.