templatekw: add compatdict() as a replacement for showdict()
This is mostly a copy of showdict(), which will be deprecated later. See
the docstring for why it's called a "compat" dict.
showenvvars() is ported to the new API as an example.
# 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