Allow switching tabs with scroll wheel.

[DrewNaylor]

Code available in this Gist:
https://gist.github.com/DrewNaylor/b2d79180090f8fd5d1dfd0dda2d39c06

Copied here in case something happens to it:

    Private Sub tabcontrolAboutWindow_MouseWheel(sender As Object, e As MouseEventArgs) Handles tabcontrolAboutWindow.MouseWheel
        ' Getting the mouse scroll direction was based on this SO answer:
        ' https://stackoverflow.com/a/2378365

        ' Allows the tabs to be scrolled with the mouse, like in many
        ' Linux applications.
        ' Perhaps this could be made into a sub with args for easier reuse.

        ' Ensure the mouse isn't in the tabpage itself.
        ' This is based on this SO answer:
        ' https://stackoverflow.com/a/21098227
        Dim tabpage As TabPage = tabcontrolAboutWindow.SelectedTab
        If Not tabpage.ClientRectangle.Contains(tabpage.PointToClient(Control.MousePosition)) Then

            If e.Delta > 0 Then
                ' If scrolling down, go left.
                If tabcontrolAboutWindow.SelectedIndex - 1 = -1 Then
                    ' If the next tab is out of bounds, select the last tab.
                    tabcontrolAboutWindow.SelectTab(tabcontrolAboutWindow.TabCount - 1)
                Else
                    ' Otherwise, select the tab to the left.
                    tabcontrolAboutWindow.SelectTab(tabcontrolAboutWindow.SelectedIndex - 1)
                End If
            Else
                ' If scrolling up, go right.
                If tabcontrolAboutWindow.SelectedIndex + 1 > tabcontrolAboutWindow.TabCount - 1 Then
                    ' If the next tab is out of bounds above the usable tab indexes,
                    ' select the first tab.
                    tabcontrolAboutWindow.SelectTab(0)
                Else
                    ' Otherwise, select the next tab to the right.
                    tabcontrolAboutWindow.SelectTab(tabcontrolAboutWindow.SelectedIndex + 1)
                End If
            End If
        End If
    End Sub

[DrewNaylor]

libscrollswitchtabs from the drews-libs project can be used to make things more compact.