Dropped num_indexes field -- this is always a function of mem and val len
tsdb_flush function

This is used to flush to and sync the db to disk.
More notes
Ensure test causes bucket growth
OOM traced as errors
Fixed wrong slot_duration ref
Simplify struct fields
Refactor tsdb_goto_epoch

The previously supported flags have been simplified to cover two
cases: failing when an epoch doesn't exist and growing an epoch
on demand.

Epochs are always loaded lazily for writes -- they are never
created directly in the call to goto.

Read only mode might not be properly supported at this point.
Updated notes