Labels can be associated with events and can have
display properties such as a description and colour,
this is why we need an endpoint for the client to
retrieve them.
Events may be filtered by sequence(s):
…/event?sequence=1
…/event?sequence=1;3;7
Events may be filtered by date:
…/event?date0=1970-01-01
Events may be filtered by a date interval:
…/event?date0=1970-01-01&date1=1980-01-01
Events may also be paginated.
If the configuration file is not found, either at its
default place ($HOME/etc/www/config.json) or wherever
indicated by the DOUGAL_API_CONFIG environment variable,
create a temporary default config and try to run with it.
On the other hand, if we are in production (NODE_ENV == production)
we exit with non-zero in the absence of a real configuration file.
