Removed `--print-sample-lua-writer`, added `--print-default-data-file`.

Closes #943.
Added module for writing python scripts, with several examples.

See scripts subdirectory.
Commented python modules/sample scripts.
Added graphviz.py example script.
Improved graphviz.py.

It won't regenerate images that have already been built.
Print stderr output of filters to stderr.
Added scripts/abc.py.
Minor code reformatting in script examples.
Added scripts/tikz.py.
Small code cleanup.
pandoc.py: Fixed bug for {}, removed rawInline, rawBlock.
Updated for removed unMeta, unFormat in pandoc-types.
Makefile:  Remove *everything* on 'make veryclean'.
adding support for breve accents via \u{} while reading LaTeX
Shared:  Better error message when default data file not found.

Listing the full path can confuse people who are using
`--self-contained`:  they might have intended the file to be
found locally.  So now we just list the data file name.
Merge branch 'master' of https://github.com/semorrison/pandoc
Improved INSTALL instructions:

* Note binary package for OSX.
* Added URL of github wiki page on installing the dev version.
LaTeX reader missing \oe and \OE characters
Merge pull request #950 from semorrison/master

LaTeX reader missing \oe and \OE characters
Added *~ and *.pyc to .gitignore.