The following headers need to be split into declarations and definitions (.h and .cpp):

• mvSliderItems.h
• mvDragItems.h
• mvInputItems.h
• mvAboutWindow.h
• mvMetricsWindow.h
• mvPopup.h

This can be completed over individual pull requests.

In web version, update function void OpenShellURL(const std::string& url) to open link in a new browser tab.

Is your feature request related to a problem? Please describe.
Standard mode has the usual keystrokes for notepad, but there are more that would probably be useful.

Describe the solution you'd like
As a first step, a quick review of the common keystrokes in notepad/wordpad/work, for example might throw up some obvious ones we could add