Add typespecs to the prototype actions and elements
Add `make dialyzer` and dialyzer to reltool.cfg
Single reltool cfg base, with overlay merged in during build

Now there will be a single reltool_base.config file, which when being
built, will have the overlay sections of reltool_BACKEND.config and/or
reltool_PLATFORM.config merged in.

Also update travis build rules.