Bump version to 0.31

Enable java 8

Bump version to 0.29

Bump version to 0.28

Cleanup some Android Studio lint warnings

Bump version to 0.26

Bump version to 0.25

Bump version to 0.24

Guard against possible leak pre android-24

From Android Studio lint:

On versions prior to Android N (24), initializing the WifiManager via
Context#getSystemService can cause a memory leak if the context is not
the application context.
In many cases, it's not obvious from the code where the Context is coming
from (e.g. it might be a parameter to a method, or a field initialized
from various method calls). It's possible that the context being passed in
is the application context, but to be on the safe side, you should consider
changing context.getSystemService(...) to
context.getApplicationContext().getSystemService(...).

Bump version to 0.22