Reformat source code with IntelliJ IDEA preset

Some of this may be slightly off but it's better than it was
Merge pull request #152 from Kobata/style-reformat

Reformat source code with IntelliJ IDEA preset
Update README.md, add CONTRIBUTING.md

Signed-off-by: Steven Downer <grinch@outlook.com>
Add modifed google style checkstyle.xml

Commented-out things are features that require unreleased versions
of checkstyle.
Github's urls are case-sensitive
Fix documentation of PluginManager.getPlugin

It is looking up by ID, not name
Add IntelliJ formatting setting xml file
Added subscription to VoxelEvent
Merge pull request #8 from SpongePowered/master

merge