Merge pull request #1 from csmith/master

Start work on a generic link extractor.
Add JSR305

Use @Nonnull
Merge pull request #5 from greboid/jsr305

Add JSR305
Switch CI to j8
Merge pull request #6 from greboid/java8

Switch CI to j8
Remove travis.
Merge pull request #7 from greboid/java8

Ditch travis
Tell gradle to use 1.8.