The reason for refactoring was to accommodate
Multiseis / client sequence exports, which will be
served by this endpoint via a specific Content-Type.
In the process, the cache has been fixed and redesigned.
Related to #12.
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.
