When merged, this will become alpha4.

Users should set the spyder preference "Run" to "Execute in a dedicated console" to avoid having multiple vpython programs run in the same view.

Each program the user runs opens in a separate browser tab. That is unavoidable. Ideally, t user would close those tabs between runs.

With this PR:

• There is a message printed when vpython is imported if the user has the wrong Run setting. Screenshot is below.
• When the browser tab is closed and the user is running in spyder, magic is done behind the scenes to force vpython to be re-imported the next time the code is run.
• Pushing run multiple times on the same program without closing the browser tab results in displaying the same things multiple times (once for each time you hit run). Not sure I can fix that.

Screenshot of warning message printed in spyder console: