Pom.xml removed; build instructions deprecated

[gharman]

The pom.xml file was removed in commit 5959981 breaking the maven build instructions in the readme and on ground-context.org.

I see sbt artifacts in the project - if a switch to sbt was intentional then the documentation needs to be updated; else pom.xml should be put back.

[kevinji]

I believe a switch to sbt is intentional, but pinging @vsreekanti just to be sure.

[vsreekanti]

Sorry for the inconsistency, @gharman. We're in a state of high flux right now, and a couple things have slipped through the cracks. I'll update the build instructions on the website ASAP.