contrib: add new examples area and start it out with a config for `hg fix` This is the configuration contributors should use for our C/C++ code. I expect to expand this file as we get more automated formatter oversight. Differential Revision: https://phab.mercurial-scm.org/D6872

[fix]
clang-format:command = clang-format --style file -i
clang-format:pattern = (**.c or **.cc or **.h) and not "listfile:contrib/clang-format-ignorelist"