bug#29367: 27.0.50; State and doc of `inline'

[Drew Adams]

> > What is the purpose of 'inline'?
> > 'inline' appears to be an alias for 'progn'.
> > Does it have some magic difference?
> 
> The purpose seems to be to let the byte compiler inline
> function calls for efficiency reasons.

In that case, it would seem to correspond to what, in
Common Lisp, would be a declaration (`declare').

In Common Lisp, declarations are supposed to be
documented, even when implementation-specific.  They
are something a user provides, so users need to know
about them.