v0.5.0

Full Changelog: v0.4.0...v0.5.0

v0.4.0

use the typing features starting from python 3.9;
update translator APIs with better names and types, example features need not be tensors;
modify the FieldAwareTranslator to match the API change;
update the Field APIs to match the translator new API names;
modify the SeqField to match the Field API;
remove the NullableTensor custom type;
remove useless hyperparameters predefined in the very earlier versions;
add the optimizer hyperparameters defaulted to Adam;
refactor the Updater API by removing the parameters to the constructor and the unimplemented class method;
update the Training and Testing Updaters to match changes to the abstract interface by simplifying the init and class-method constructor;
add a optimizer selection function to simplify the training updater factory method;
add a new kwarg to the training updater factory method to support customized optimizers not defined in the new selection function;
refactor the Training and Testing updaters for clearer logic and easier inheriting by renaming methods and introducing a mixin that fetches and builds batches with new translator APIs;
remove the dry-run and skip argument from TrialBot;
rename the vocab-dump arg to vocab-path that better reflects its usage;
add the feature that infers the snapshot path and vocab path in test mode on the model filename specified;
remove the vocab saving when running the loop and only save the vocab at the time when it's created;
add the default priority for adding event handler;