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
Fixed IE11 JS errors

Closes issue #1022.
Thanks to mattlee78 for pointing this out.
Possibly fixed crash when HOME is undefined

When HOME was undefined on Linux, the code would try calling
os.listdir(None) which will obviously fail.

This is a workaround. A proper fix would be to rewrite the
code to check for each operating system, not a combination
of operating systems, environment variables and the current
air humidity in London.
Updated "Installing Textures" section

Use 1.7.2 in the examples instead of 1.6.2, since a 1.7 version is required