Merge pull request #17 from tambeti/gradle

Add gradle build support
Add some directives to upload to Maven Central

taken straight from
http://www.vandalsoftware.com/post/52468430435/publishing-an-android-library-aar-to-a-maven
Try not to kill build hosts

Remove the -j argument from ndk-build in gradle build file, it meant "allow
infitie jobs". Build hosts unfortunately have finite resources.
Merge pull request #19 from jobi/maven-central

Add some directives to upload to Maven Central
Merge pull request #18 from tambeti/fixes

Try not to kill build hosts
Remove maven and ant build files
Merge pull request #21 from litl/remove-maven

Remove maven and ant build files
Use NDK path for finding ndk-build

Read NDK path from local.properties or from ANDROID_NDK_HOME env variable.