Libkml

This PR adds libkml as a tool target. It compiles on Linux and OSX, but is having difficulties on Windows. @jan76 and I have been making progress on this latter part.

I forked libkml from google and made some fixes targeted towards Linux and Windows builds. I'd appreciate some reports on whether this compiles on a variety of platforms. So far it compiles on Mint, OSX 10.7.4, OSX 10.8.2, and whatever @solidgoldbomb uses.