adding 2019 arXMLiv resources, and tidying up page references and notes

_posts/2019-09-19-arxmliv-2019-dataset-release.md

resources/arxmliv-dataset-082017.md

resources/arxmliv-dataset-082018.md

resources/arxmliv-dataset-082019.md

resources/arxmliv-embeddings-082017.md

resources/arxmliv-embeddings-082018.md

resources/arxmliv-embeddings-082019.md

resources/arxmliv.md

resources/index.md

technical.md