Move /etc/dhcpcd.conf to /etc/dhcpcd/dhcpcd.conf

Move /etc/dhcpcd.conf to /etc/dhcpcd/dhcpcd.conf

Rationale: packages want to drop hook scripts into /etc
Having /etc/dhcpcd now allows us to have /etc/dhcpcd/enter-hooks.d
and /etc/dhcpcd/exit-hooks.d which allows this.

Users can also now create symlinks from installed example hooks
into /etc rather than having to edit a singular file.

Fixes #494.