Hepdata-validator

Wrap `RefResolutionError` exception: see [PR](https://github.com/HEPData/hepdata-validator/pull/21) from Sinclert.

* Include work by Sinclert on supporting remote JSON schemas.
* New `JsonSchemaResolver` and `HTTPSchemaDownloader` objects.
* Don't invalidate an empty `errors` list in `DataFileValidator`.
* Check that each value of `cmenergies` keyword is numeric.
* Allow `data_schema` and `table_doi` keys in `submission.yaml` file.
* Bump native HEPData schema version to 1.0.1 after these changes.
* Improve metadata pushed to [PyPI](https://pypi.org/project/hepdata-validator/) for tagged releases.

* Ensure JSON schema files from new location are included in pip package.
* Use Travis CI to automatically deploy tagged releases on PyPI.

The JSON schema distributed with the last `hepdata-validator` 0.1.16 release have been given a version number 0.1.0. This release 0.2.0 includes improved JSON schema with a version number 1.0.0 which catch a number of common mistakes made by data submitters. This release 0.2.0 is now compatible with both Python 2 and Python 3.

schema and yaml: correct bugs in schema and use safe YAML load/dump

* schema: rename some "id" values, and fix a major bug where the value of "items" was given as an array of one JSON schema, thereby only validating the first element of a list instead of *all* elements in the list.
* testsuite: fix test data to match newly corrected schema.
* yaml: always use SafeLoader and SafeDumper or preferably the corresponding LibYAML classes if installed.
* yaml: simplify validation of parser errors by catching a generic Exception rather than yaml.parser.ParserError and IOError, also now implicitly catching a yaml.constructor.ConstructorError caused by the presence of "!!python/unicode" tags.
* version: bump to 0.1.16.

Signed-off-by: Graeme Watt <graeme.wattdurham.ac.uk>

validator: catch exceptions, allow absence of comment, bump version

* Catch ParserError and IOError exceptions when loading YAML files.
* Allow a submission.yaml file without an initial "comment" key.
* Add tests to give 100% coverage.
* Bump version to 0.1.15.

Signed-off-by: Graeme Watt <graeme.wattdurham.ac.uk>