Load huge file

Database files can potentially be huge (>10Mo, assume no maximum). As a HERA database is just a large in-memory object, it is possible to run up against the string length limitation (assume 512MB). This can make use of JSON.stringify a no-go. Plus, JSON.loads can be really slow on such files, and might block the current thread.

Thus, file loading should:

1. support arbitrarily large files
2. NOT block the current thread
3. be as fast as possible