add gitignore from https://github.com/github/gitignore

[natejenkins]

Hi, thanks for this library!

Adding a .gitignore would make commits much cleaner, I copied the example Android .gitignore from https://github.com/github/gitignore (CC0 1.0 license) as a starting point.

[natejenkins]

Personally I would add a few more files to this gitignore. When building this project the following files and folders are created:

	.idea/
	gradle/
	gradlew
	gradlew.bat

In general I add the gradle folder and files to the repo and ignore ./idea/*

thoughts?