Added documentation for show and cancel.
Added documentation for show and cancel.

(cherry picked from commit 9197ffd07dc93c1d462ce56b3295b4e920769b6e)

Scandit/barcodescanner-sdk-cordova,Scandit/barcodescanner-sdk-cordova,Scandit/barcodescanner-sdk-cordova,Scandit/barcodescanner-sdk-cordova