Updates on Code & Markdown writer

Widget.Caret
1) Create a Caret widget, to be used among writers.

Writer.Markdown
1) Markdown support Container defined caret
2) Implement focus()
3) Implement .range()
4) Implement caretOut event

Writer.Code
1) support Container defined caret
2) Implement .range() to get/set selection/caret in editor
3) Implement caretOut event, to allow caret movement among writers

WriterContainer
1) Universal Caret shared by all writers
2) allow caret movement among writers.