spec/ace: further volume clarifications
spec/ace: further volume clarifications

- Standardise on definite article when referring to ACE
- Establish that multiple overlapping volumes (with coonflicting
  targets) should not be permitted
- Drop the ACE-creating-files-on-the-host to a SHOULD NOT

iaguis/appc-spec,appc/spec,3ofcoins/appc-spec,3ofcoins/appc-spec,apcera/appc-spec,krnowak/appc-spec,squeed/spec,apcera/appc-spec,jonboulle/spec,jonboulle/spec,dgonyeo/spec,squeed/spec,krnowak/appc-spec,iaguis/appc-spec,squeed/spec,dgonyeo/spec,krnowak/appc-spec,iaguis/appc-spec,appc/spec,appc/spec,jonboulle/spec,dgonyeo/spec,apcera/appc-spec,3ofcoins/appc-spec