fileset: extract function that builds initial subset from ctx or status
This function will be used to recalculate subset when mctx.ctx is switched.
# See http://EditorConfig.org for the specification
root = true
[*.py]
indent_size = 4
indent_style = space
trim_trailing_whitespace = true
[*.{c,h}]
indent_size = 8
indent_style = tab
trim_trailing_whitespace = true