Added manual POI option

Here's how to use it:
have a list called "manualpois" in your config filled with objects that contain
the attributes id, x, y and z. Feel free to add more attributes as you need them.
Then, write filter functions to filter for your custom POIs (hint: use the id).
manualpois is now a per-render option
Added possibility to return tuple from filterfunc

If the returned type is a tuple, it will be interpreted as first the
title (i.e. hovertext), then the content of the infowindow. If the
returned type is a string, it will be used as both the title and
infowindow content (the old behaviour). This means that older configs
are still compatible and need no changes.
Don't print scary traceback when textures cannot be found

See #860
Converted the IOErrors i missed before
Merge pull request #858
Better manualPOI validator
specifying a directory name for a dimension should work now
updated tileset.py and genPOI.py and a few other stragglers
Add less verbose config option
updaded doc download links
Merge in pull request #865
Merge Pull Request #859
Allow unicode to be returned from a genPOI filter function
Updated documentation

* Added paragraph and example about returning tuples from a filter
  (Issue #859)

* Added section about manualpois
  (Issue #858, Issue #869, Issue #598)

* Fixed a typo in the FAQ

* Added logging to file to the FAQ
  (Issue #871)
use git to find current hash, should work with overviewer-as-submodule
JSObserver will show ETA, and the 'renderComplete' message will persist

Closes #784
Closes #786
Merge in pull request #872
Merge pull request #862
Make sure that regionset.type always has a value