Loading ontologies fails (for me) in 2.4.4

Hi!
I updated to the latest version (from 2.something<2) but immediately ran into trouble testing in a fresh venv:
```
>>> psi = pronto.Ontology.from_obo_library("psi-ms.obo")
Traceback (most recent call last):
File "", line 1, in
File "/tmp/pronto/lib/python3.6/site-packages/pronto/ontology.py", line 207, in from_obo_library
f"http://purl.obolibrary.org/obo/{slug}", import_depth, timeout, threads
File "/tmp/pronto/lib/python3.6/site-packages/pronto/ontology.py", line 283, in __init__
cls(self).parse_from(_handle) # type: ignore
File "/tmp/pronto/lib/python3.6/site-packages/pronto/parsers/rdfxml.py", line 89, in parse_from
raise ValueError("could not find `owl:Ontology` element")
ValueError: could not find `owl:Ontology` element
```
so I tried with something from the docs:
```
>>> apo = pronto.Ontology.from_obo_library("apo.obo")
thread '' panicked at 'assertion failed: `(left != right)`
left: `0`,
right: `0`: Python threading is not initalized and the `auto-initialize` feature is not enabled.

Consider calling `pyo3::prepare_freethreaded_python()` before attempting to use Python APIs.', /tmp/pip-req-build-o2_6liwv/build/temp.linux-x86_64-3.6/cargo/registry/src/github.com-1ecc6299db9ec823/pyo3-0.15.1/src/gil.rs:233:21
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Traceback (most recent call last):
File "", line 1, in
File "/tmp/pronto/lib/python3.6/site-packages/pronto/ontology.py", line 207, in from_obo_library
f"http://purl.obolibrary.org/obo/{slug}", import_depth, timeout, threads
File "/tmp/pronto/lib/python3.6/site-packages/pronto/ontology.py", line 283, in __init__
cls(self).parse_from(_handle) # type: ignore
File "/tmp/pronto/lib/python3.6/site-packages/pronto/parsers/obo.py", line 18, in parse_from
doc = fastobo.iter(handle, ordered=True)
pyo3_runtime.PanicException: assertion failed: `(left != right)`
left: `0`,
right: `0`: Python threading is not initalized and the `auto-initialize` feature is not enabled.

Consider calling `pyo3::prepare_freethreaded_python()` before attempting to use Python APIs.
```
which left me with more unknowns, so I tried from local obo to rule out connection or networking-lib issues:
```
>>> psi = pronto.Ontology('psi-ms.obo')
thread '' panicked at 'assertion failed: `(left != right)`
left: `0`,
right: `0`: Python threading is not initalized and the `auto-initialize` feature is not enabled.

Consider calling `pyo3::prepare_freethreaded_python()` before attempting to use Python APIs.', /tmp/pip-req-build-o2_6liwv/build/temp.linux-x86_64-3.6/cargo/registry/src/github.com-1ecc6299db9ec823/pyo3-0.15.1/src/gil.rs:233:21
Traceback (most recent call last):
File "", line 1, in
File "/tmp/pronto/lib/python3.6/site-packages/pronto/ontology.py", line 283, in __init__
cls(self).parse_from(_handle) # type: ignore
File "/tmp/pronto/lib/python3.6/site-packages/pronto/parsers/obo.py", line 18, in parse_from
doc = fastobo.iter(handle, ordered=True)
pyo3_runtime.PanicException: assertion failed: `(left != right)`
left: `0`,
right: `0`: Python threading is not initalized and the `auto-initialize` feature is not enabled.

Consider calling `pyo3::prepare_freethreaded_python()` before attempting to use Python APIs.
```
The errors differ, but I assume they still might be connected somewhere. What could it be?