Improve the handling of <meta> tags for charset decleration, supports HTML 5 format and generates a more accurate output.
No longer opens the item when shift or ctrl key is down (for multiple selection).
Fixed an issue that "Save Again" prompts multiple windows.
Fixed an issue that a multiple-item capture process freezes when meeting a meta refresh which redirects to an non-existent page (404 etc).
"Clear Highlights in the Selection" now clears all ScrapBook additions. Also adjusted related language and optimized related codes.
Fixed a leak that empty <span> tags are still generated at the start of selection which is accidentally located at the end of an element.
Fixed multiple issues concerning editor undo and change notice.

- Multiple ScrapBook page tabs in a common window now have separated undo history and change detection, instead of sharing common ones.
- Fixed an issue that undo malfunctions if a window is closed or a page with undo history has been switched to another page.
- Fixed an issue that editing inline annotation, editing sticky note, or dragging sticky note may not be recorded and undone correctly if the previous editing is on another tab.
- The Undo button no longer be disabled again, but instead, shows an alert message if no history is available.
- @TODO: if a page with undo history is moved to another window, it is lost permanently.
- @TODO: closing background tabs that are changed do not receive an alert for saving.