Merge branch 'pw/3.0-commentchar-auto-deprecation'
"core.commentChar=auto" that attempts to dynamically pick a
suitable comment character is non-workable, as it is too much
trouble to support for little benefit, and is marked as deprecated.
* pw/3.0-commentchar-auto-deprecation:
commit: print advice when core.commentString=auto
config: warn on core.commentString=auto
breaking-changes: deprecate support for core.commentString=auto