Rename .api._load._maybe_schema to try_to_load_schema to make its
purpose clearer.

…ose were added into tests.backend.test_properties

…erties

…scape_char

…rseline

Various fixes and enhancements may close #135

…parse

….utils.get_path_and_ext

Fix/issue 139: process cases that pathlib.Path.resolve fails on errors in .ioinfo.utils.get_path_and_ext

fix: add a packaging configuration to distribute type hints data

Add python 3.10, the latest stable version, support.

Feature/py310 support

Remove 'devel' sub package from options.extras_require because it's not
very useful.

Add python 3.10 as a test target environment in github actions.

Rebase the test default target environment to python 3.10.

Add an workaround for the github actions issue that python 3.10 as
wrongly interpreted as python 3.1.

Mak py310 as the default test target environment

Apply some more strict flake8 rules with its extensions and fixes for
the followings.

- E126 rule, continuation line over-indented for hanging indent
- W504 rule, line break after binary operator
- E121, continuation line under-indented for hanging indent
- E123, closing bracket does not match indentation of opening bracket's
  line
- E241, multiple spaces after ','

Feature/more code style checks