Use doctemplates 0.2.1: allows $-- line comments in templates.

Closes #3806.

MANUAL.txt

@@ -1643,6 +1643,9 @@ and modifying your custom templates accordingly. An easy way to do this
 is to fork the [pandoc-templates] repository and merge in changes after each
 pandoc release.
 
+Templates may contain comments:  anything on a line after `$--`
+will be treated as a comment and ignored.
+
 [pandoc-templates]: https://github.com/jgm/pandoc-templates
 
 Pandoc's Markdown

pandoc.cabal

@@ -334,7 +334,7 @@ library
                  JuicyPixels >= 3.1.6.1 && < 3.3,
                  Glob >= 0.7 && < 0.9,
                  cmark-gfm >= 0.1.1 && < 0.2,
-                 doctemplates >= 0.1 && < 0.2,
+                 doctemplates >= 0.2.1 && < 0.3,
                  http-client >= 0.4.30 && < 0.6,
                  http-client-tls >= 0.2.4 && < 0.4,
                  http-types >= 0.8 && < 0.10,

stack.pkg.yaml

@@ -18,12 +18,12 @@ packages:
   extra-dep: false
 extra-deps:
 - pandoc-types-1.17.2
-- texmath-0.9.4.4
 - hslua-0.9.0
 - skylighting-0.4.1
 - cmark-gfm-0.1.1
 - QuickCheck-2.10.0.1
 - tasty-quickcheck-0.9.1
-- haddock-library-1.4.3
 - hs-bibutils-6.2.0.1
-resolver: lts-9.1
+- doctemplates-0.2.1
+- haddock-library-1.4.3
+resolver: lts-9.9

stack.yaml

@@ -8,11 +8,11 @@ packages:
 - '.'
 extra-deps:
 - pandoc-types-1.17.2
-- texmath-0.9.4.4
 - hslua-0.9.0
 - skylighting-0.4.1
 - cmark-gfm-0.1.1
 - QuickCheck-2.10.0.1
 - tasty-quickcheck-0.9.1
+- doctemplates-0.2.1
 - haddock-library-1.4.3
-resolver: lts-9.1
+resolver: lts-9.9