Log messages routed to stdout/stderr as appropriate.

This also uses a dedicated logger instead of passing everything to the
root logger. `overviewer_core` still needs to be updated to reflect
this.

Additionally, `logger.configure` has been simplified.
Using a dedicated logger inside overviewer_core.
docstring for InverseLevelFilter added.
Removed second logger.

The root logger for "overviewer" is now named "`overviewer_core`".
Fixed log format reconfiguration regression.

Commit c991135 introduced a regression where it was no longer possible
to re-configure the loggers once they had been set up. This is now
fixed.
Fixed a crash when redirecting stdout.
Fixed the way texture.py searched for foliage, grass and chests textures.
This is a "quick-and-dirty fix", you may improve it as I'm novice in Python.
Default files in data/textures have been renamed to reflect changes in new 1.6 texture packs (aka resource packs)
Merge branch 'master' of git://github.com/overviewer/Minecraft-Overviewer
Added genPOI workaround for MystCraft

Possibly fixes issue #993.
Update the genPOI to uses multiple processes
Cleanup even more
Merge branch 'master' of git://github.com/overviewer/Minecraft-Overviewer
Tried a fix for normal.png being not found on Travis + added logs
removed logs
Removed dev logs
trying to fix Travis build about chest texture not found. When normal.png from texture pack not found, fall back to chest.png
Fix #993
Overviewer now require 1.7 textures or newer
Minor doc cleanups
Fix link errors on OSX 10.9?  I think?

Fix for #1008