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
Merge branch 'master' of https://github.com/spongepowered/Sponge into config
Serialize configs.