Add support for python3

Libreoffice 4.0 will switch its internal python version to 3.3.0
so it's to support that.

Porting done automatically 2to3 plus print_function import added
manually. Tested on both libreoffice master with internal python
and with libreoffince 3.6.4 on debian with system python 2.7.

This bumps the minimal python version to 2.6 since 2.5 does not
have the print function.
Fixing Issue #120 (When converting odt to pdf table of contents may have wrong page numbers)

Issue: https://github.com/dagwieers/unoconv/issues/120

I added cycle to update indexes two times.
Fixing fix for issue #120

indexes.getByIndex(i).update() must be called second time
after second call to
    document.refresh()
    indexes = document.getDocumentIndexes()
Add XLSX support

add the 'Calc MS Excel 2007 XML' (XLSX) export filter
Merge pull request #131 from mondayx/patch-1

Add XLSX support
Merge pull request #117 from ojwb/master

Fix documentation typos
Merge pull request #127 from peterdemin/master

Third attempt to make pull request for fixing issue #120
#133 fix export to non existent directory
Merge pull request #111 from xrmx/master

Add python 3 support
Update README.asciidoc

I had a problem when using unoconv with Nginx and PHP-FPM.

I finally solved the issue with the help rendered here.

https://github.com/dagwieers/unoconv/issues/87#issuecomment-18800070

So I am adding the fix so that anyone after me can quickly realize the issue.
make sure LOdev gets new param styles
Merge pull request #144 from clkao/master

make sure LOdev gets new param styles
Update unoconv
Merge pull request #154 from zopyx/master

Find LibreOffice 4.1 on MacOSX
add Microsoft Works (.wps) import filter
Merge pull request #140 from simkimsia/patch-1

Update README.asciidoc
Merge pull request #134 from gazofnaz/master

#133 fix export to non existent directory
Merge pull request #159 from josiasmontag/patch-2

add Microsoft Works (.wps) import filter
Correct output of "make help"