Merge pull request #16 from cKlee/master

dropped Offering, new Service Ontology
Merge pull request #19 from cKlee/master

extended introduction, equivalents gr:Location <=> schema:Place, gr:hasStockKeepingUnit <=> schema:sku
Merge pull request #24 from cKlee/master

removed inCollection: maybe introduce later
added some mappings to Bibframe
added purl for ontology
Merge pull request #1 from dini-ag-kim/master

update from dini-ag-kim