saugns v0.3.6e. (Re-tag.) Bugfixes, minor clean-up.

This replaces the hasty v0.3.6e tag. Back to -std=c99,
-pedantic removed, but the warning fixes included.
(The -v version is also now increased.)

Fix crash on opening several files
when only some failed to open.

Fix numerical expression parsing for
several subtractions in a row.

Simplify usage notice, update man page.

(These changes are part of work included
in an experimental redesign, in branches
named beginning with mgs. Far from done,
but will be the basis for new versions.)
This tag has no release notes.