Add `empty_paragraphs` extension.

* Deprecate `--strip-empty-paragraphs` option.  Instead we now
  use an `empty_paragraphs` extension that can be enabled on
  the reader or writer.  By default, disabled.

* Add `Ext_empty_paragraphs` constructor to `Extension`.

* Revert "Docx reader: don't strip out empty paragraphs."
  This reverts commit d6c58eb836f033a48955796de4d9ffb3b30e297b.

* Implement `empty_paragraphs` extension in docx reader and writer,
  opendocument writer, html reader and writer.

* Add tests for `empty_paragraphs` extension.

3 files changed, 9 insertions, 18 deletions

diff --git a/test/docx/0_level_headers.native b/test/docx/0_level_headers.native
index 973f4cfe5..804ad8732 100644
--- a/test/docx/0_level_headers.native
+++ b/test/docx/0_level_headers.native
@@ -1,15 +1,15 @@
 [Table [] [AlignDefault] [0.0]
  [[]]
- [[[Plain []]]
+ [[[]]
  ,[[Plain [Str "User\8217s",Space,Str "Guide"]]]
- ,[[Plain []]]
- ,[[Plain []]]
- ,[[Plain []]]
+ ,[[]]
+ ,[[]]
+ ,[[]]
  ,[[Plain [Str "11",Space,Str "August",Space,Str "2017"]]]
- ,[[Plain []]]
- ,[[Plain []]]
- ,[[Plain []]]
- ,[[Plain []]]]
+ ,[[]]
+ ,[[]]
+ ,[[]]
+ ,[[]]]
 ,Para [Str "CONTENTS"]
 ,Para [Strong [Str "Section",Space,Str "Page"]]
 ,Para [Str "FIGURES",Space,Str "iv"]
diff --git a/test/docx/comments.native b/test/docx/comments.native
index 8587b54dd..3357bc257 100644
--- a/test/docx/comments.native
+++ b/test/docx/comments.native
@@ -1,4 +1,4 @@
 [Para [Str "I",Space,Str "want",Space,Span ("",["comment-start"],[("id","0"),("author","Jesse Rosenthal"),("date","2016-05-09T16:13:00Z")]) [Str "I",Space,Str "left",Space,Str "a",Space,Str "comment."],Str "some",Space,Str "text",Space,Str "to",Space,Str "have",Space,Str "a",Space,Str "comment",Space,Span ("",["comment-end"],[("id","0")]) [],Str "on",Space,Str "it."]
 ,Para [Str "This",Space,Str "is",Space,Span ("",["comment-start"],[("id","1"),("author","Jesse Rosenthal"),("date","2016-05-09T16:13:00Z")]) [Str "A",Space,Str "comment",Space,Str "across",Space,Str "paragraphs."],Str "a",Space,Str "new",Space,Str "paragraph."]
 ,Para [Str "And",Space,Str "so",Span ("",["comment-end"],[("id","1")]) [],Space,Str "is",Space,Str "this."]
-,Para [Str "One",Space,Span ("",["comment-start"],[("id","2"),("author","Jesse Rosenthal"),("date","2016-05-09T16:14:00Z")]) [Str "This",Space,Str "one",Space,Str "has",Space,Str "multiple",Space,Str "paragraphs.",Space,Str "\182",Space,Str "\182",Space,Str "See?"],Str "more",Span ("",["comment-end"],[("id","2")]) [],Str ".",Space,Str "And",Space,Str "this",Space,Str "is",Space,Str "one",Space,Str "with",Space,Str "a",Space,Span ("",["comment-start"],[("id","3"),("author","Jesse Rosenthal"),("date","2016-06-22T14:35:00Z")]) [Str "Do",Space,Str "something."],Span ("",["comment-start"],[("id","4"),("author","Jesse Rosenthal"),("date","2016-06-22T14:36:00Z")]) [Str "Do",Space,Str "something",Space,Str "else."],Str "comment",Space,Str "in",Space,Str "a",Space,Str "comment",Span ("",["comment-end"],[("id","3")]) [Span ("",["comment-end"],[("id","4")]) []],Str "."]]
+,Para [Str "One",Space,Span ("",["comment-start"],[("id","2"),("author","Jesse Rosenthal"),("date","2016-05-09T16:14:00Z")]) [Str "This",Space,Str "one",Space,Str "has",Space,Str "multiple",Space,Str "paragraphs.",Space,Str "\182",Space,Str "See?"],Str "more",Span ("",["comment-end"],[("id","2")]) [],Str ".",Space,Str "And",Space,Str "this",Space,Str "is",Space,Str "one",Space,Str "with",Space,Str "a",Space,Span ("",["comment-start"],[("id","3"),("author","Jesse Rosenthal"),("date","2016-06-22T14:35:00Z")]) [Str "Do",Space,Str "something."],Span ("",["comment-start"],[("id","4"),("author","Jesse Rosenthal"),("date","2016-06-22T14:36:00Z")]) [Str "Do",Space,Str "something",Space,Str "else."],Str "comment",Space,Str "in",Space,Str "a",Space,Str "comment",Span ("",["comment-end"],[("id","3")]) [Span ("",["comment-end"],[("id","4")]) []],Str "."]]
diff --git a/test/docx/drop_cap_nostrip.native b/test/docx/drop_cap_nostrip.native
deleted file mode 100644
index ea6a244b5..000000000
--- a/test/docx/drop_cap_nostrip.native
+++ /dev/null
@@ -1,9 +0,0 @@
-[Para [Str "Drop",Space,Str "cap."]
-,Para []
-,Para [Str "Next",Space,Str "paragraph."]
-,Para []
-,Para [Str "Drop",Space,Str "cap",Space,Str "in",Space,Str "margin."]
-,Para []
-,Para []
-,Para []
-,Para [Str "Drop",Space,Str "cap",Space,Str "(not",Space,Str "really)."]]