Fixed empty reference links.  Closes #1186.

Includes test.
LaTeX reader:  Better error messages with include files.

Closes #1274.

Rewrote handleIncludes.

We now report the actual source file and position where the error
occurs, even if it is included.  We do this by inserting special
commands, `\PandocStartInclude` and `\PandocEndInclude`, that encode
this information in the preprocessing phase.

Also generalized the types of a couple functions from
`Text.Pandoc.Parsing`.
LaTeX reader: Fixed regression introduced with last commit.

Tests now pass again.
Distinguish tight and loose lists in Docbook output

Determined by the first block of the first item being Plain.
DocBook writer:  Small tweaks to last commit.

* Use isTightList from Shared.
* Adjust writer test, since isTightList is a bit different from what
  was used before.

Closes #1250.
AsciiDoc writer: Correctly handle empty table cells.

Closes #1245.
AsciiDoc writer:  Added test for empty table cells.
AsciiDoc writer:  Handle multiblock table cells.

Closes #1246.
README: Note about `unnumbered` being added to final 'References' sect.
Added Tests.Writer.AsciiDoc to repository.
Markdown reader: Fixed bug with unwanted code in lists.

Closes #1154.

When reading a raw list item, we now strip off nonindent
spaces.
Added test for #1154.
Docx writer:  Added ability to give fallback in parseXml.
Docx writer:  Fall back on distribution reference.docx.

* Undid changes to parseXml in last commit.
* Instead of a string fallback, we have parseXml fall back
  on the reference.docx that comes with pandoc if the user's
  reference.docx does not contain a needed file.
* Closes #1185.
Clarified use of `--natbib` and `--biblatex`.

Not for use with pandoc-citeproc.
README: Clarified citation key syntax.
LaTeX writer: Fixed inconsistencies with reference escaping.

- toLabel is now monadic, and it does the needed string escaping.
- Closes #1130.
Fixed the fix to #1154.

We need to strip off up to 4 spaces, not up to 3.
Updated changelog.
make_osx_package: Use cpphs to avoid problems with clang cpp.

See https://github.com/jgm/pandoc/issues/1172