Cl-sii

- (PR 242, 2021-10-12) rtc: Verify outermost XML signature of SII AECs
- (PR 247, 2021-10-19) config: Update Python version used in CI jobs to 3.8.12
- (PR 245, 2021-10-20) rtc.parse_aec: Convert to `None` the empty optional values in the Caratula

- (PR 238, 2021-09-08) rut: Fix RUT clean method to accept '0-0' value
- (PR 241, 2021-09-16) rtc: Make AEC field 'nombre persona autorizada cedente' optional

- (PR 234, 2021-08-09) dte: Convert stdlib dataclasses into pydantic dataclasses
- (PR 236, 2021-08-09) DteXmlData: Restore mistakenly deleted regression tests

- (PR 228, 2021-06-29) config: Update Python version used in CI jobs to 3.8.10
- (PR 230, 2021-07-09) dte: Convert stdlib dataclass `DteXmlData` into pydantic dataclass

- (PR 226, 2021-06-15) requirements: Remove Django upper bound constraint
- (PR 224, 2021-06-15) requirements: Upgrade 'Django'
- (PR 223, 2021-06-08) requirements: Upgrade 'Django'
- (PR 221, 2021-05-14) requirements: Upgrade Pydantic
- (PR 216, 2021-04-22) docs: Add creation of release branch to instructions for new releases
- (PR 213, 2021-04-21) build(deps): bump toml from 0.10.1 to 0.10.2

- (PR 195, 2021-04-15) build(deps): bump requests from 2.23.0 to 2.25.1
- (PR 212, 2021-04-14) config: Update Python version used in CI jobs to 3.8.9
- (PR 210, 2021-04-13) rtc.data_models_aec: remove validation for the progression of
'monto_cesion' across the 'cesiones'
- (PR 207, 2021-04-08) build(deps): bump virtualenv from 20.0.31 to 20.4.3
- (PR 208, 2021-04-08) rtc.data_models_aec: remove match validation for 'fecha_firma_dt' and
'fecha_cesion_dt'
- (PR 205, 2021-03-26) build(deps): bump lxml from 4.6.2 to 4.6.3
- (PR 204, 2021-03-24) requirements: Upgrade 'Django'