Don't notify EngineJobs of failures more than once

Fixes #97.
Don't notify jobs of failures decoding from cache.

Since we also try to reload the image from source,
we may end up reporting first a failure and then
a success which would leave the request in an
undefined state.
Fix some comments: - typos, - documented empty blocks, - shortened some {@link}s, - converted some multi-line comments to single-line/javadocs.
Only send to Sonatype on bump repo/3.0a branch.
Add travis build status to readme.
Make sure check style runs on Android sources.

Fixes #104
Fix sonatype publish script.
Move env variables to travis settings.
Make library compile/test/checkstyle on Windows (@Ignore in comments where needed)
Close streams correctly and make DiskLruCacheWrapperTest method independent with random.
Simplify some thenAnswers
Move all ArrayDeque (API 9+) creations to Util.createQueue.
Change @TargetApi and SDK_INT comparison constants to named constants from Build.VERSION_CODES.
Fix application RequestManager always being paused
Make .gradle files a little more uniform with 'strings'
Suppress less checkstyle checks in tests (no need for javadocs)
and fix the errors.
Clean up .gitignore re:local.properties
Bump roboelectric plugin version.
exceptions--
Less declared but not used exceptions.
Less tested but never thrown exceptions.
Missing keywords.