Improve our filter documentation

Closes #278

See merge request !1112

This patch also uncovered the fact that our test_filter_deps_ok() test
has been inaccurate. Thus the element built in this test
(deps-permitted.bst) has been modified so that it build depends on the
input.bst element, as it should.

tests/filter.py: Ensure deps_ok test passes

Fail when we explictly try to include/exclude non-existent domains in a filter element

See merge request !1117

Providing a remote will limit build's pull/push remote actions to
the given remote specifically, ignoring those defined via user or
project configuration.

Add --remote, -r option to bst build, inline with pull & push

See merge request !1119

The 'wallclock-us' is a option that we thought we already had.