Fix sidenote alignment in lists.

[WesleyAC]

The 5% difference is due to the difference in the width of the p
elements and the ul/ol elements: 55% and 50%, respectively.

Fixes #170.

[msyds]

This only works at a very specific window size, since the widths of normal paragraphs still grow at a different rate than the widths of li paragraphs. While less portable, the following heuristic had much better results for me:

diff --git a/tufte.css b/tufte.css
index c9b2528..d052517 100644
--- a/tufte.css
+++ b/tufte.css
@@ -190,7 +190,7 @@ section > table {
 section > dl,
 section > ol,
 section > ul {
-    width: 50%;
+    width: calc(55% - 40px);
     -webkit-padding-start: 5%;
 }

@@ -449,3 +449,9 @@ label.margin-toggle:not(.sidenote-number) {
         width: 100%;
     }
 }
+
+li .sidenote,
+li .margin-note {
+    /* it's so close lol */
+    transform: translateX(4px)
+}