Rename alwaysPreventDefault option to preventDefaultKeys
Call preventDefault on contextmenu DOM event to allow right-click

Migrated over from deathcap/kb-bindings@ea6c195e390f73a150b3533af84e8ab4382f72dd:

Allows right-click to be used for other purposes. This default
preventing can be turned off with opts preventDefaultContext: false.
0.3.0