Update squish library to 1.11
Updating libpng to v1.5.14 and zlib to v1.2.7

Since libpng has a dependency upon zlib, both updates were combined for one commit/pull-request.
Merge pull request #250 from thecelloman/updatelibpngandzlib

Updating libpng to v1.5.14 and zlib to v1.2.7
Merge pull request #243 from thecelloman/updatesquish

Update squish
Update TinyXML to v2.6.2
Merge pull request #255 from thecelloman/updatetinyxml

Update TinyXML to v2.6.2