Refactor space handling of writers

I went through the issues of goorgeous and picked a few that seemed easy enough
to add (and added some fore as todos for later). That helped a lot and showed
some bugs / edge cases that required changes.

- the org writer wrote a lot of eol spaces and just removed it whenever
  String() was actually called. That worked until now but did not bode with
  rendering an empty headline - by removing ALL eol space we would render "* "
  back as just "*" -> not a headline anymore.
- the html writer had some special handling for line spacing inside paragraphs
  and list items - with the introduction of more blocks we need that handling
  everywhere.
  As browsers / html renderers are nice enough to collapse whitespace (and
  especially collapse "\s*\n" into " ") we can just write out the newlines and
  let the renderer take care of the rest.

org/testdata/example.org

@@ -70,6 +70,46 @@ with multiple lines
 #+BEGIN_QUOTE
 Mongodb is very webscale
 #+END_QUOTE
+
+** issues from goorgeous (free test cases, yay!)
+*** DONE [[https://github.com/chaseadamsio/goorgeous/issues/29][#29:]] Support verse block
+#+BEGIN_VERSE
+This
+*is*
+verse
+#+END_VERSE
+
+#+BEGIN_CUSTOM
+or even a *totally* /custom/ kind of block
+crazy ain't it?
+#+END_CUSTOM
+*** DONE [[https://github.com/chaseadamsio/goorgeous/issues/47][#47:]] Consecutive ~code~ wrapped text gets joined
+either ~this~ or ~that~ foo.
+either ~this~
+or ~that~ foo.
+*** DONE [[https://github.com/chaseadamsio/goorgeous/issues/68][#68]]: Quote block with inline markup
+#+BEGIN_QUOTE
+[[www.example.com][/this/ *is* _markup_!]]
+#+END_QUOTE
+
+*** DONE [[https://github.com/chaseadamsio/goorgeous/issues/77][#77]]: Recognize =code=--- as code plus dash
+*** DONE [[https://github.com/chaseadamsio/goorgeous/issues/75][#75]]: Not parsing nested lists correctly
+- bullet 1
+  - sub bullet
+*** DONE [[https://github.com/chaseadamsio/goorgeous/issues/78][#78]]: Emphasis at beginning of line
+/italics/
+
+
+Text
+/italics/
+*** DONE [[https://github.com/chaseadamsio/goorgeous/issues/82][#82]]: Crash on empty headline
+**** 
+just a space as title...
+*** DONE [[https://github.com/chaseadamsio/goorgeous/issues/84][#84]]: Paragraphs that are not followed by an empty line are not parsed correctly
+**** Foo
+Foo paragraph.
+**** Bar
+Bar paragraph
 ** Footnotes
 - normal footnote reference [fn:1]
 - further references to the same footnote should not [fn:1] render duplicates in the footnote list