Bug#889814: lintian: Improve long description of epoch-change-without-comment

[Jeremy Bicha <jbicha@debian.org>]

To help reduce the need to use an epoch later, I think we should
recommend packages with date-based numbering use a version number
prefixed with something like 0~. For instance, the current version of
fonts-noto-color-emoji in Debian is 0~20180102-1. This could possibly
be a Lintian warning if a date-based format is detected for a new
Debian package.

Some packages can avoid the use of an epoch by using an epoch only for
the specific packages that need an epoch by manipulating
dh_gencontrol. For instance, this is done in fonts-ubuntu to use
epochs only for the transitional packages (which we'll be able to drop
in a few months).

https://salsa.debian.org/fonts-team/fonts-ubuntu/blob/debian/unstable/debian/rules

This trick is probably only useful when a package changes names (like
gcompris will probably become a transitional package depending on
gcompris-qt soon and only the gcompris package needs the epoch).

Thanks,
Jeremy Bicha