investigate OpenFDA as a data source for compound properties

[andrewsu]

The OpenFDA API may be a useful source of quantitative compound properties (e.g., "overlay" in the parlance of Translator). This ticket is related to another ticket on OpenFDA at biothings/biothings_explorer#131.

The OpenFDA API is described at https://open.fda.gov/apis/. The primary key is UNII. For example, drug report for afatinib (UNII: 41UD74L59M) is at https://api.fda.gov/other/substance.json?search=unii:%2241UD74L59M%22 .

The Properties section has some interesting pharmacokinetic parameters. Might be useful in the context of "overlaying" information that might be useful to some users.

Referencing is very good, with statement-level references to primary literature, databases, documents from FDA/WHO, etc.