Add a draft for a standard module style guide

[mppf]

Add a draft for a standard module style guide

This PR adds a draft standard module style guide as an aid for the effort of stabilizing the standard modules.
Based in large part upon #6698.

Discussed with lots of people but final review is by @bradcray - thanks!

[gbtitus]

This looks like a fine start. You might add a section saying that in modules that are strictly providing access to other interfaces (as for example Sys provides POSIX), the symbol capitalization should match that of the external interface.

[bradcray]

Thanks for taking a start at this, Michael. Other than the comments above, this looks good to me and captures the sorts of things I agree that we've generally agreed upon. No other obvious cases leapt to mind, but I'll keep thinking about it as we proceed.

[mppf]

FYI for those who have already commented @vasslitvinov pointed out a guidance piece to add to it

A property method needs to be parenthesized if it is named isXXX or hasXXX, otherwise it should be paren-less.

I plan to incorporate this.

[mppf]

@bradcray - I've created a version incorporating people's feedback. Could you have a final look at it before I merge it? Thanks.

[bradcray]

I think this is good to go as a starting point, thanks!