Migrate and Improvement

[FarshidRoohi]

• Migrate to Kotlin and Androidx
• Null Safety
• And Bug Fix #33

  Fatal Exception: java.lang.ArrayIndexOutOfBoundsException: length=10; index=-1
     at java.util.ArrayList.get(ArrayList.java:439)
     at com.goodiebag.pinview.Pinview.onTextChanged(Pinview.java:440)
     at android.widget.TextView.sendOnTextChanged(TextView.java:10052)
     at android.widget.TextView.setText(TextView.java:5921)
     at android.widget.TextView.setText(TextView.java:5759)
     at android.widget.EditText.setText(EditText.java:122)
     at android.widget.TextView.setText(TextView.java:5716)
     at com.goodiebag.pinview.Pinview.setValue(Pinview.java:331)
     at com.goodiebag.pinview.Pinview.clearValue(Pinview.java:312)