Gokart

fix

- Fix `ListTaskInstanceParameter` behavior when not specific requires method : 195

Now works following:

class Foo(gokart.TaskOnKart): hasn't requires method
foo = gokart.ListTaskInstanceParameter()

def run(self):
foo = self.load_data_frame('foo')

New feature

- Support no specification load single dataframe 180

class Task(gokart.TaskOnKart):
bar = gokart.TaskInstancePrameter()

def run(self):
df = self.load_data_frame() We won't have to write "bar" about it because it's obvious

BUGFIX
* make s3 config singleton (178) mski-iksm
* support python 3.9 (173) hirosassa

Refactoring
* fix minor deps (175) hirosassa
* Feature/use isort (177) mski-iksm
* fix badges and cleanup whitespace (174) hirosassa

minor fix and improve CI
- Suppress redundant warning messages by mski-iksm
- tox test for multiple python versions by hirosassa

Changes

- packaging setup.py -> poetry

New Feature
* Feature/efficient task lock 162 by mski-iksm