jatsgenerator 0.6.0

Modified: jatsgenerator.cfg configuration file includes a new property elocation_id_pattern for how to generate an elocation-id value
Modified: generate.py various changes to not add empty XML tags when data is not available, while retaining backwards compatibiltiy for the previous XML generation ability
Modified: generate.py can also add peer review <sub-article> tags including some metadata, and add a <pub-history> tag and multiple <event> tags, if the data is given
Added: build.set_publication_history() to add <pub-history> tag and one or multiple <event> tags inside it
Added: build.set_sub_articles() to add one or multiple <sub-article> tags
Added: build.set_sub_article() to populate a <sub-article> tag

Code merged in PR #48