Fixed an absolute reference to SpongeAPI.

This enables building Sponge as a subproject of another Gradle build. I'm assuming this was an oversight since the other references from the same file were relative.
Update README.md
Merge pull request #38 from teozkr/hotfix/sponge-as-subproject

Enable building Sponge as a subproject of something else
Merge pull request #45 from jacklin213/patch-1

Update README.md
Added method from ASMUtils to AMSHelper
Merge pull request #44 from Raphfrk/asm_helper

More asm helper methods
Forge Event Handling change
  Removes directly accessing the forge ListenerLists
  Registers one EventListenerHolder for each event type/priority with forge
  EventListenerHolders are generated dynamically using ASM
  The event listener holder calls all the sponge listeners
  Priorities are grouped since Sponge has more priorities than forge