Add support for NullAway

[leinardi]

It would be nice to have support for the Error Prone's plugin NullAway. It is getting really popular and is quite useful to help eliminate NullPointerException.

The console output looks like this:

:sample:compileReleaseNdk NO-SOURCE
:sample:processReleaseJavaRes NO-SOURCE
/home/travis/build/leinardi/FloatingActionButtonSpeedDial/library/src/main/java/com/leinardi/android/speeddial/SpeedDialActionItem.java:162: error: [NullAway] initializer method does not guarantee @NonNull field mLabel is initialized along all control-flow paths (remember to check for exceptions or early returns).
        public Builder(@IdRes int id, @DrawableRes int fabImageResource) {
               ^
    (see http://t.uber.com/nullaway )
/home/travis/build/leinardi/FloatingActionButtonSpeedDial/library/src/main/java/com/leinardi/android/speeddial/SpeedDialActionItem.java:175: error: [NullAway] initializer method does not guarantee @NonNull field mLabel is initialized along all control-flow paths (remember to check for exceptions or early returns).
        public Builder(@IdRes int id, @Nullable Drawable drawable) {
               ^
    (see http://t.uber.com/nullaway )
2 errors

My guess is that shouldn't be too different to parse than the base Error Prone error.

[tomasbjerre]

I added that output and tried with the Error Prone parser and I think it looks good. Did you try that?

[leinardi]

You are right, this is working, I guess the report were missing because I got the errors on old code and I have commentOnlyChangedContent set to true.

Thanks again for the nice plugin 👍

PS
Any chance you can have a look at #34