Add slim release support for runner script
Add slim marker file as automatic overlay
Change nodetool path to under releases/<RELEASE_VERSION>/
Add TODO comment to install_upgrade script template
Bump rebar version to 2.3.1
Update release notes for 2.3.1
Merge pull request #52 from shino/slim-release-support

Slim release support
Add {prefix, atom()} option for abnfc_opts

Specify the atom to use as a prefix for the decoder and generator
functions inside the parser's module.  Default is ''.
Add {parser, module()} option for abnfc_opts

Specify the module to use for parsing the ABNF grammars.  Default is
'abnfc_rfc4234'.
Add {qc, proplist()} option for abnfc_opts

Specify the options to use for the generator functions inside the
parser's module.  Default is [].