Pii-data

* added "extra" field to PiiEntity
* added add_process_stage() method to PiiEntity
* added chunks() method to PiiChunkIterator
* added dump_yaml() function
* fixed exception hierarchy
* fix: error message when opening file
* fix: in text dump protect against chunk with no text

* PiiEnum base type changed to IntEnum
* PiiEnum.STREET_ADDRESS changed to PiiEnum.LOCATION, with STREET_ADDRESS
left as alias
* PiiCollection improvements:
- add_detectors() method
- to_json() method, to make it directly serializable by CustomJSONEncoder
* fix: PiiCollection clone should also clone the detector map
* fix: only create a JSON encoder in PiiCollection if needed

* fix: Dummy logger class

* fix: ensure loaded PiiCollection objects have integer ids for Detectors
* fix: only add lang to PiiCollection header if defined

* PiiEntityInfo made immutable
* added clone() class method to PiiCollection
* refactored & improved config reading
* new functionality in helper.io: read remote files
* json dump parameters modified
- allow no-indent specification
- only close output file if we opened it
- allow additional formatting arguments
* added logger wrapper

* DocumentChunk class refactored into a full class, with equality method and
asdict()
* Refactored dump code; dump to JSON
* when dumping documents to JSON & YAML dump non-structural context fields
(and skip structural context)
* modified tree & sequence iteration: changed automatic id assignment
* new class method from_dict() in PiiInstance
* when reading a PiiCollection from file, recreate PiiInstance objects
* wrapper load() method for PiiCollectionLoader
* add_chunk() method for LocalSrcDocument objects (sequence, table & tree)
* new LocalSrcDocumentFile dispatcher class
* openfile: allow file-like objects as argument
* fixed newlines in text output
* added json dump to object
* added config file management
* new PiiEnum values
* refactored PiiEntity; new PiiEntityInfo subclass
* special SrcDocument metadata field "default_lang"
* added "lang" context field to DocumentChunk, automatically copied from
document "default_lang" if not present
* some bugfixes