Fixed crashes with malformed MCA files.

Some tools write MCA files that are not 4K-aligned, these caused a crash.
extended mob spawn detection to spawn inside transparent blocks

With Minecraft spawning it is possible to spawn on top of blocks with
solid top surface and 2 blocks clear space above. Up to now the clear
space was tested only with air, but also other transparent blocks allow
mobs to spawn inside (e.g. button, flower or thin snow).
Now both cases are handled correctly.
added Iron Trapdoor from 14w07a
added default suffix for world save to PNG

fix #34: now a default suffix ".png" is added when a filename without a
suffix was given.
fixed crash at bottom of map

The pointers for spawn detection inside transparent blocks could be
invalid at the bottom layer of the map. Now all sections have an
additional check.
ID definition update for 14w08 + 14w25a

14w08a Trapdoors are now called "Wooden Trapdoor"
14w25a added Coarse Dirt, Sponge, Wet Sponge, Prismarine, Prismarine
Bricks, Dark Prismarine, Sea Lantern
derived colors from wiki
Fixed block ID colors

Added Podzol
In the past commits I used an average color sampling resulting in much
too dark colors, now everything looks better as it is now based on the
vanilla textures.
fixed bid/mask bug with upside down slabs

Upside down slabs were not found in the BlockIdentifier cache, as the
.mask was not applied before bid calculation.
Block ID updates

14w30a banners
14w31a inverted daylight sensor
14w32a red sandstone +chiseled +smooth +slabs +stairs
"double smooth slabs" are renamed to "full slabs"
Merge pull request #36 from EtlamGit/SaveAddMissingPNG

added default suffix for world save to PNG
Merge pull request #33 from EtlamGit/master

New renderer implementation for Mob Spawning
Merge pull request #31 from madmaxoft/master

Fixed crashes with malformed MCA files.
Merge remote-tracking branch 'upstream/master' into ControllingTheDepthSlider