[Don't Pull] Add support for uploading additional artifacts to CurseForge

:warning:  ___Don't pull this yet, CurseForge has an issue with their API that prevents this from working, once fixed all should be good___
![IRC](http://i.imgur.com/RihZFF9.png)

---

## This change adds the ability to upload multiple artifacts to CurseForge per build. 

### Backwards compatibility
The main artifact can still be changed via:
```groovy
curse {
    artifact = myOtherJarTask
}
```
As well, the default artifact is still the obfuscated jar.
This keeps compatibility with existing gradle scripts.

### An example of the new configuration:
```groovy
curse {
    apiKey = project.curseForgeAPIKey
    projectId = 12345
    changelog = 'I made a change!'
    releaseType = 'release'

    additionalArtifact sourceJar, javadocJar, deobfJar
    additionalArtifact file("$project.buildDir/libs/A-Custom-File.txt")
}
```

### Some Notes:
* Additional artifacts are uploaded with the main artifact being their `parentFile`. This means that these additional artifacts will never be the "Primary Download" on the CurseForge website.
* Additional artifacts are intended to be files that are related to the current build, but not the main obfuscated jar. (Source jars, deobfuscated jars, javadoc jars, changelog files, etc)