Tempsdb

with slicing chunks in `VarlenSeries`
* added extra comparison operators for `VarlenEntry`
* added `sync` to `VarlenSeries`
* fixed a bug with not propagating metadata write exceptions
* fixed a bug with `Database` treating `varlen` and metadata as real time series

* added logging for opening and closing series

* added the context manager syntax to VarlenIterator
* fixed a memory leak that happened during getting current value
from an empty series
* added `MemoryPressureManager` support for `Database`

* fixed an issue with `Iterators`

* **bugfix**: fixed some bugs with reading values after close
* added support for storing metadata as minijson
* this will be enabled by default is minijson is importable
* fixed minor compiler warnings
* `TimeSeries.iterate_range` will accept a parameter called
`direct_bytes` for compatibility with `VarlenSeries`.
It's value is ignored
* more class constructors use explicit typing - faster tempsdb
* `TimeSeries.get_current_value` will correctly raise `ValueError` instead of returning None

* older TempsDB databases that do not support varlens will be updated upon opening
* added metadata support for databases
* a flush will be done before re-enabling mmap
* bugfix to read archive data