Add a new API plugin for AGR

[tokebe]

This PR addresses #28 by adding a new manifest plugin.

Example output, click to expand

{
  "_id": "WB:WBGene00003163",
  "agr": {
    "taxon": "NCBITaxon:6239",
    "species_name": "Caenorhabditis elegans",
    "symbol": "mdl-1",
    "is_implicated_in": [
      {
        "doid": "DOID:14330",
        "term_name": "Parkinson's disease",
        "evidence_code": "ECO:0000270",
        "evidence_code_name": "expression pattern evidence used in manual assertion",
        "reference": "PMID:20091141",
        "date": "20140106",
        "source": "WB"
      },
      {
        "doid": "DOID:14330",
        "term_name": "Parkinson's disease",
        "evidence_code": "ECO:0007013",
        "evidence_code_name": "combinatorial experimental and author inference evidence used in manual assertion",
        "reference": "PMID:20091141",
        "date": "20140106",
        "source": "WB"
      }
    ],
    "implicated_via_orthology": [
      {
        "doid": "DOID:10283",
        "term_name": "prostate cancer",
        "with_orthologs": [
          "HGNC:7534"
        ],
        "evidence_code": "ECO:0000501",
        "evidence_code_name": "evidence used in automatic assertion",
        "reference": "MGI:6194238",
        "date": "20210326",
        "source": "Alliance"
      },
      {
        "doid": "DOID:3512",
        "term_name": "neurofibrosarcoma",
        "with_orthologs": [
          "HGNC:7534"
        ],
        "evidence_code": "ECO:0000501",
        "evidence_code_name": "evidence used in automatic assertion",
        "reference": "MGI:6194238",
        "date": "20210326",
        "source": "Alliance"
      },
      {
        "doid": "DOID:5041",
        "term_name": "esophageal cancer",
        "with_orthologs": [
          "RGD:3128"
        ],
        "evidence_code": "ECO:0000501",
        "evidence_code_name": "evidence used in automatic assertion",
        "reference": "MGI:6194238",
        "date": "20210326",
        "source": "Alliance"
      },
      {
        "doid": "DOID:3458",
        "term_name": "breast adenocarcinoma",
        "with_orthologs": [
          "RGD:3128"
        ],
        "evidence_code": "ECO:0000501",
        "evidence_code_name": "evidence used in automatic assertion",
        "reference": "MGI:6194238",
        "date": "20210326",
        "source": "Alliance"
      }
    ]
  }
}