internal function name

[Karim-Mane]

@bahadzie - has suggested to harmonise on internal function names.
When he was reviewing {cleanepi}, he realised that the internal functions are differently named (do not start with .) in comparison to some other packages where they start with .. Below is his comment:
"One thing I've noticed in some of our other repos is a name convention starting with a . for internal function e.g..is_order for this particular one."

I am bringing the discussion here as this might affect other packages too. And would like people to give their opinions between these 2 naming conventions and potentially add the reasonning behing their choice.