Add Signals

[collerek]

• Breaking: QuerySet bulk_update method now raises ModelPersistenceError for unsaved models passed instead of QueryDefinitionError
• Breaking: Model initialization with unknown field name now raises ModelError instead of KeyError
• Added Signals, with pre-defined list signals and decorators: post_delete, post_save, post_update, pre_delete,
  pre_save, pre_update
• Add py.typed and modify setup.py for mypy support
• Performance optimization
• Updated docs

[codecov-io]

Codecov Report

Merging #66 (7dd892e) into master (1d4a074) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            master       #66    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files           69        73     +4     
  Lines         5902      6235   +333     
==========================================
+ Hits          5902      6235   +333     

Impacted Files	Coverage Δ
ormar/decorators/property_field.py	100.00% <ø> (ø)
ormar/__init__.py	100.00% <100.00%> (ø)
ormar/decorators/__init__.py	100.00% <100.00%> (ø)
ormar/decorators/signals.py	100.00% <100.00%> (ø)
ormar/exceptions.py	100.00% <100.00%> (ø)
ormar/models/metaclass.py	100.00% <100.00%> (ø)
ormar/models/model.py	100.00% <100.00%> (ø)
ormar/models/newbasemodel.py	100.00% <100.00%> (ø)
ormar/queryset/queryset.py	100.00% <100.00%> (ø)
ormar/signals/__init__.py	100.00% <100.00%> (ø)
... and 8 more