bump version to 0.19.0-dev in develop after branching release/0.18.0
Merge branch 'release/0.18.0' into develop

Conflicts:
	eulxml/__init__.py
logic to generate CERP xml from python email Message (adapted from rushdieweb) [#31164691] #reviewthis branker
preliminary travis-ci config
Merge branch 'develop' of https://github.com/emory-libraries/eulxml into develop
travis-ci config
move travis config into correct location
split out optional requirements from "dev" requirements for travis-ci
update travis config to use optional reqs instead of dev
fix issue where validation errors were collecting/repeating
move dev/opt requirements entirely into setup.py
switch to nose for unit tests
update readme test example to use an eulxml test
add travis-ci build status to readme
remove references to deleted testcore
pep8/linter whitespace cleanup
try setting an empty http proxy for schema loading in unit tests
skip schema-validation tests when no HTTP_PROXY is set
revert empty proxy env for unit tests
revise command for installing dev deps