Textile reader: Improved link parsing.

In particular we now pick up on attributes. Since pandoc links
can't have attributes, we enclose the whole link in a span
if there are attributes.

Closes #1008.
Org reader: Precise rules for the recognition of markup

The inline parsers have been rewritten using the org source code as a
reference. This fixes a couple of bugs related to erroneous markup
recognition.
Add .editorconfig

Use EditorConfig to define a some basic styling rules for code.  This
should also help to reduce the number of commits introducing trailing
whitespace.

See http://editorconfig.org/ for details.
Force failure of a Travis build if GHC produces warnings

Pandoc should, as stated in CONTRIBUTING.md, always compile without
warnings.  This patch forces GHC to treat warnings like errors during
Travis builds, making it possible to catch mistakes (like missing
top-level type definitions) early.
Merge pull request #1226 from tarleb/org-emphasis-reader

Org reader: Precise rules for the recognition of markup
Merge pull request #1227 from tarleb/editorconfig

Add .editorconfig
Merge pull request #1228 from tarleb/travis-fail-on-warnings

Force failure of a Travis build if GHC produces warnings
Updated travis script to test with multiple GHC versions.
Fixed $CABAL in travis script.
More travis changes.
More travis tweaks.
Travis: install hsb2hs.
Travis build: remove 6.12; add -v2 to dependencies install.
More travis tweaks.
More travis tweaks.
Travis: gave up trying to test the sdist.

For some reason hsb2hs was not found, even though it was built.
More travis tweaks.
Fixed cabal path in travis config.