src/Text/Pandoc/Writers/LaTeX.hs: Use \texorpdfstring for section
captions.
Update tests suite to expect \texorpdfstring.
RST Reader: Warn about skipped directives

move `addWarning` to Parsing.hs, so it can be used by Markdown & RST readers.
expose warnings from RST reader; refactor

This commit moves some code which was only used for the Markdown Reader
into a generic form which can be used for any Reader.  Otherwise, it
takes naming and interface cues from the preexisting Markdown code.
RST: literal role should produce Code,

code role should have "code" class.

http://docutils.sourceforge.net/docs/ref/rst/roles.html says that
`text`:literal` is the same as ``text``.  docutils outputs a <literal>
element in both cases, whereas for the code role, it outputs a <literal>
element with the "code" class.
RST reader: improve support for custom roles

- Add "sourceCode" to classes for :code: role, and anything inheriting
  from it.
- Add the name of the custom role to classes if the Inline constructor
  supports Attr.
- If the custom role directive does not specify a parent role, inherit
  from the :span: role.

This differs somewhat from the rst2xml.py behavior.  If a custom role
inherits from another custom role, Pandoc will attach both roles' names
as classes.  rst2xml.py will only use the class of the directly invoked
role (though in the case of inheriting from a :code: role with a
:language: defined, it will also provide the inherited language as a
class).
WIP: tests for RST roles
RST Reader: compute Attrs when role is defined

Move recursive role lookup from renderRole to addNewRole.  The Attr value
will be the same for every occurance of this role, so there's no reason
to compute it every time.  This allows simplifying the
stateRstCustomRoles map considerably.

We could go even further, and remove the fmt and attr arguments to
renderRole, which are null except for custom roles.
RST: warn about ignored fields in role directives
Fixe autolinks with following punctuation.

Closes #1811.
The price of this is that autolinked bare URIs can no longer
contain `>` characters, but this is not a big issue.
Org reader: properly handle links to `file:target`

Org links like `[[file:target][title]]` were not handled correctly,
parsing the link target verbatim.  The org reader is changed such that
the leading `file:` is dropped from the link target.

This is related to issues #756 and #1812.
Merge pull request #1813 from tarleb/file-links

Org reader: properly handle links to `file:target`
DocBook reader: handle keycombo, keycap.

Closes #1815.
DocBook reader:  get string content in inner tags for literal elements.

Closes #1816.
DocBook reader: Handle menuchoice elements better.

They are now rendered with a `>` between them.
Closes #1817.
DocBook readers:  Include id on section headers.

Closes #1818.
Merge pull request #1805 from bergey/rst

RST Reader - Improved Role Support
Added a note about the need for `-s` to include YAML in Markdown output.

Closes #1715. Thanks to @nichtich for the suggestion.
Merge branch 'use-texorpdfstring' of https://github.com/wilx/pandoc into wilx-use-texorpdfstring

Conflicts:
	src/Text/Pandoc/Writers/LaTeX.hs
	tests/Tests/Writers/LaTeX.hs
Improved texorpdfstring patch #1148.

* Make LaTeX reader recognize texorpdfstring.
* Don't use texorpdfstring unless it's actually needed.
* Fix tests.