Rename suffix to tag as it ends up not being the filename suffix,
apply that tag to .o and .d files so that changing the build type
does not wipe/reuse files from another build type.
Make .d file hidden files, this does not seem possible for the .o
files as they are targets and posix support inference rules when only
the suffix changes. This is not a big issue as Kakoune ignores those
files by default.
