Smarter smart quotes.

Treat a leading " with no closing " as a left curly quote.
This supports the practice, in fiction, of continuing
paragraphs quoting the same speaker without an end quote.
It also helps with quotes that break over lines in line
blocks.

Closes #7216.

test/command/7216.md

@@ -0,0 +1,19 @@
+```
+pandoc -t latex
+"This is some text in quotes. Another paragraph by the same speaker follows. The first paragraph should have no close quote.
+
+"The second paragraph should have open and close quotes."
+
+| "Open quote on this line,
+| Close quote on the next line."
+| "Quotes on the same line."
+^D
+``This is some text in quotes. Another paragraph by the same speaker
+follows. The first paragraph should have no close quote.
+
+``The second paragraph should have open and close quotes.''
+
+``Open quote on this line,\\
+Close quote on the next line.''\\
+``Quotes on the same line.''
+```

test/command/pandoc-citeproc-320a.md

@@ -49,17 +49,13 @@ references:
 Foo [@item1; @item2; @item3; @item4; @item5; @item6; @item7; @item8].
 ^D
 Foo (al-ʾUdhrī, n.d.; al-ʿUdhrī, n.d.; al-\'Udhrī, n.d.; al-'Udhrī,
-n.d.; al-'Udhrī, n.d.; Uch, n.d.; Uebel, n.d.; Zzz, n.d.).
+n.d.a, n.d.b; Uch, n.d.; Uebel, n.d.; Zzz, n.d.).
 
 ::: {#refs .references .csl-bib-body .hanging-indent}
 ::: {#ref-item6 .csl-entry}
 Uch, Ann. n.d.
 :::
 
-::: {#ref-item4 .csl-entry}
-'Udhrī, Jamīl al-. n.d.
-:::
-
 ::: {#ref-item1 .csl-entry}
 ʾUdhrī, Jamīl al-. n.d.
 :::
@@ -72,8 +68,12 @@ Uch, Ann. n.d.
 \'Udhrī, Jamīl al-. n.d.
 :::
 
+::: {#ref-item4 .csl-entry}
+'Udhrī, Jamīl al-. n.d.a.
+:::
+
 ::: {#ref-item5 .csl-entry}
-'Udhrī, Jamīl al-. n.d.
+---------. n.d.b.
 :::
 
 ::: {#ref-item7 .csl-entry}