dev-util/astyle: spliting into sub-slots

dev-util/astyle: spliting into sub-slots

As dev-util/astyle-3.1 has changed interfeces compared with -3.0.1
spliting into sub-slots "0/3.0" and "0/3.1" introduced.

This can be usefull to rebuild packages that depends on astyle
if it's sub-slot updates.

E.g. codeblocks-17.12 could use system installed astyle-3.0.x
and incompatible with astyle 3.1 without codeblocks Astyle plugin patching.
So it's will need to rebuild codeblocks if user for some reason want
to have astyle-3.1 and use codeblocks.

Also dev-util/astyle-3.0.1-r1.ebuild creates "libastyle.so" symlink now
during installation like for dev-util/astyle-3.1 to avoid linking error
during compilation with using "-lastyle" key.

Signed-off-by: Matthias Maier <tamiko@gentoo.org>
Closes: https://github.com/gentoo/gentoo/pull/8585