Org reader: Use specialized org parser state

The default pandoc ParserState is replaced with `OrgParserState`.  This
is done to simplify the introduction of new state fields required for
efficient Org parsing.
Org reader: Fix parsing of nested inlines

Text such as /*this*/ was not correctly parsed as a strong, emphasised
word.  This was due to the end-of-word recognition being to strict as it
did not accept markup chars as part of a word.  The fix involves an
additional parser state field, listing the markup chars which might be
parsed as part of a word.
Org reader: Provide more language identifier translations

Org-mode and Pandoc use different language identifiers, marking source
code as being written in a certain programming language.  This adds more
translations from identifiers as used in Org to identifiers used in
Pandoc.

The full list of identifiers used in Org and Pandoc is available through
http://orgmode.org/manual/Languages.html and `pandoc -v`, respectively.
Org reader: Support inline images
Shared.openURL:  Set proxy with value of http_proxy env variable.

Note:  proxies with non-root paths are not supported,
because of limitations in http-conduit.

Closes #1211.
Merge pull request #1219 from tarleb/org-images

Org-reader: support inline images, clean-up code, fix bugs
Fixed PDF print function in reveal.js template.

Closes #1220.  Thanks to kevinkenan.
Org reader:  Added type signature.
Make it possible to run filters that aren't executable.

Pandoc first tries to find the executable (searching the path
if path isn't given).  If it fails, but the file exists and has
a .py, .pl, .rb, .hs, or .php extension, pandoc runs the filter
using the appropriate interpreter.

This should make it easier to use filters on Windows, and make
it more convenient for everyone.

Closes #1096.
README:  Added note to --bibtex/--natbib: not for use in making PDF.

Closes #1194. Thanks to nahoj.
Text.Pandoc.PDF:  Ensure that temp directories deleted on Windows.

The PDF is now read as a strict bytestring, ensuring that process
ownership will be terminated, so the temp directory can be deleted.
Closes #1192.
Removed whitespace at ends of lines.
Textile reader: Improved treatment of HTML spans (%).

Closes #1115.
Textile reader:  Better support for attributes.

Instead of being ignored, attributes are now parsed and
included in Span inlines.

The output will be a bit different from stock textile:
e.g. for `*(foo)hi*`, we'll get `<em><span class="foo">hi</span></em>`
instead of `<em class="foo">hi</em>`.  But at least the data is
not lost.
HTML reader:  Updated `closes` with rules from HTML5 spec.
Give more useful error message if '-t pdf' is specified.

Closes #1155.
Org reader: Minor code clean-up
Org reader: Add support for definition lists
Moved some doc files from data-files to extra-source-files.

They aren't needed at runtime.

We keep README and COPYRIGHT in data to ensure that they'll be
available on all systems on which pandoc is installed.

Closes #1123.
LaTeX reader:  handle @{} and p{length} in tabular.

The length is not actually recorded, but at least we get a table.

Closes #1180.