Have -i option understand and accept #coding declaration

Right now the interpreter ignores coding declaration (which is arguable, but that’s not this feature request). In addition, the -i option, which invokes the interpreter after processing a file, also ignores the coding declaration.

I suggest the behavior change and the invoked interpreter use the coding option.

For example, I am a pythonql http://www.pythonql.org/ user, but to run a little test of an expression requires me to write code in a file and run it, complete with print statements, in a very un-pythonesque way. It would be more natural to use the -i option and then type various debugging and experimental statements into the interpreter.

More example code at https://stackoverflow.com/questions/60266424/executing-coding-directives-in-the-python-interpreter/