Add a CSV version of the data

[frankieroberto]

The data page links to a JSON representation of all the data, but it'd also be useful to link to a CSV version, to make it easier to import into a spreadsheet.

Where there can be multiple values (eg synonyms, organisations, start pages, etc), we’ll have to decide between:

• creating separate columns (eg org1, org2, org3) and accepting that some of these will often be blank
• using a separate like | or a ; to separate multiple values within a column

Thoughts welcome!