When the Qt version is greater than 4 (so 5 at least), require the
QtWidgets module as well, which is where QWidget-based stuff lives.
Temporarily enable deprecated methods in Qt5, so there are no code
changes required.

Also pick the right poppler version, poppler-qt4 for Qt4 and
poppler-qt5 for Qt5, including the right header depending on the
version.

These changes allow katarakt to build and link, and it seems to be
working fine at a quick glance.

Now that the right include directories of poppler-qt4 are used, use the
right way to include its headers, that is without the "poppler/qt4/"
prefix.

Make use of the qmake feature for finding packages using pkg-config,
and using their results for include paths and libraries.
Also, optimize the way the version of poppler is read: query pkg-config
only once at qmake time, splitting the bits in variables added as
CFLAGS; this way, we avoids spawning 99 times (!) pkg-config and cut
during build.

All of this is done on Unix systems only, as pkg-config is available
only there.

Contrast and brightness of inverted rendering can be configured.

Thanks to thorsten!

This is required to customize it via stylesheet.

Furthermore, add documentation on how to configure vim.

This introduces the setting single_instance_per_file and
the command line flag --single-instance.

This is better for shell completion. It is now called
synctex-katarakt-vim.py

Thanks to Sergey Romanov.

Katarakt now exposes a dbus-API that allows TeX-editors to synchronize
the positions in source code and pdf via synctex.

TODO: The API allows to specify positions in the PDF as (page,x,y)
triple, but the x,y coordinates are currently ignored or set to 0,
respectively. We need more katarakt-internal API for this to be
implementable.

The file relied on a tabwidth of 4