Add exact cover fit option for device-sized cover cropping (#1254)

* Add exact cover fit option for device-sized cover cropping

* Update README to move cover cropping from FAQ to USAGE

* rename to coverfill

* edit readme

kindlecomicconverter/KCC_gui.py

@@ -329,6 +329,8 @@ class WorkerThread(QThread):
             options.noprocessing = True
         if GUI.pdfExtractBox.isChecked():
             options.pdfextract = True
+        if GUI.coverFillBox.isChecked():
+            options.coverfill = True
         if GUI.metadataTitleBox.checkState() == Qt.CheckState.PartiallyChecked:
             options.metadatatitle = 1
         elif GUI.metadataTitleBox.checkState() == Qt.CheckState.Checked:
@@ -1036,6 +1038,7 @@ class KCCGUI(KCC_ui.Ui_mainWindow):
                                            'eraseRainbowBox': GUI.eraseRainbowBox.checkState(),
                                            'disableProcessingBox': GUI.disableProcessingBox.checkState(),
                                            'pdfExtractBox': GUI.pdfExtractBox.checkState(),
+                                           'coverFillBox': GUI.coverFillBox.checkState(),
                                            'metadataTitleBox': GUI.metadataTitleBox.checkState(),
                                            'mozJpegBox': GUI.mozJpegBox.checkState(),
                                            'jpegQualityBox': GUI.jpegQualityBox.checkState(),