Implement markdown previewer.
On branch master, changes to be committed:
	modified:   html-template/htmlDoc_end.html
	modified:   html-template/htmlDoc_start.html
	modified:   html-template/stylesheet.css
	modified:   mainwindow.py
Implement themes and fix some bugs.
On branch master, changes to be committed:
	modified:   config.json
	modified:   mainwindow.py
	modified:   noteeditor.py
	modified:   quark.py
	new file:   themes/default.css
Refine syntax highlighting code by fixing some minor bugs.
On branch master, changes to be committed:
	modified:   mdhighlighter.py
Implement file opening.
On branch master, changes to be committed:
	modified:   config.json
	modified:   mainwindow.py
	modified:   noteeditor.py
Implement file saving and window title changing.
On branch master, changes to be committed:
	modified:   mainwindow.py
	modified:   noteeditor.py
Implement new note creation.
On branch master, changes to be committed:
	modified:   mainwindow.py
Implement external link handling.
On branch master, changes to be committed:
	modified:   mainwindow.py
Implement syncronized scrolling.  Known bug: when the note preview is updated, the
preview scrolls back to the top of the page.
On branch master, changes to be committed:
	modified:   mainwindow.py
Implement auto scroll preview to edited line when note is saved.
On branch master, changes to be committed:
	modified:   mainwindow.py
Reimplement auto scroll preview on save.
On branch master, changes to be committed:
	modified:   mainwindow.py
Write documentation and fix minor bugs.
On branch master, changes to be committed:
	modified:   README.md
	deleted:    html-template/stylesheet.css
	modified:   mainwindow.py
	modified:   mdhighlighter.py
	modified:   noteeditor.py
	modified:   quark.py
	modified:   quarkExtra.py