Sdmxthon

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**Added**
- Added flag for use_dataset_id on get_pandas_df

**Changes**

**Bugfixes**

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**Added**
- Added compatibility for Group on attributes related to a GroupDimensionDescriptor
- Added compatibility for SDMX-CSV on get_pandas_df and get_datasets 54
- Added reading and writing methods for Group in SDMX-ML StructureSpecific data messages

**Changes**

**Bugfixes**
- Fixed a bug on ActionEnum in DatasetAttributes

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**Added**
- Added internal enumeration for Action (ActionEnum)

**Changes**
- Changed description of dataset attributes and added docs for structure_type and unique_id in Dataset.
- Fixed reading and writing of SDMX-CSV v2 to handle ACTION column. 53
- Changed link to Changelog in docs.

**Bugfixes**
- Fixed bug when adding dataset attributes to raise an unhandled exception if not present on keys. 53

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**Added**
- Added changelog on docs and github link 52
- Structure submission to FMR from Dataflow and DataStructureDefinition 47
- Read SDMX to support SDMX-CSV v1 and v2 45
- Handling on error messages on SOAP APIs requests
- Added MessageTypeEnum documentation.

**Changes**
- Changed description of features in docs.

**Bugfixes**

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**Added**
- Added FMR interaction with data validation and metadata submission. Added methods on webservices package.
- Added SDMXError and SubmissionRequest classes to handle FMR interaction
- Added to_sdmx_csv() method to Dataset 43
- Added fmr_validation() method to Dataset 43
- Added upload_metadata_to_fmr() method to Message 44
- Added upload_metadata_to_fmr() method to API 44
- Added webservices documentation 42

**Changes**
- Changed semantic_validation to structural validation on documentation
- Changed MessageTypeEnum on StructureSpecific files from Structure to StructureSpecific

**Bugfixes**
- Fixed bug on Message validate method using old semantic_validation on each Dataset in payload.

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**Added**

**Changes**
- Support for DatasetID as key on get_pandas_df and xml_to_csv results

**Bugfixes**