This commit aims to achieve consistent stack frames control
by `stack_info` flag in logging calls the same as that in python
logging module.
Currently, both a field named `stack_info` for JsonFormatter
and `stack_info=True` for logging function are needed for
stack frames to be properly displayed.
If `stack_info` field name is not passed, no output is given
irrespective of the `stack_info` flag in logging calls.
If `stack_info=False` in logging calls and `stack_info` is also
passed as one field for JsonFormatter, the output is `{"stack_info": null}`.
Above behavior is not very consistent and requires two controls
to output stack frames. This commit makes 'stack_info' flag in logging calls
as single point control of stack frames output and there is no need to
pass `stack_info` field into JsonFormatter.

Consistent control of stack_info

feat: add support for Python 3.7

Added python2.7 EOL notice.