- Added support to rebar_prv_xref for filtering out whole module. A
  module may now be added to the list of xref_ignores in rebar.config or
  via -ignore_xref() module attribute
  - Added unit test for whole module filtering support to xref CT suite

emacs creates temp files that ends with tilde (~).
These temp files should never be commited.
It is therefore safe to ignore them.

Signed-off-by: Niklas Johansson <raphexion@gmail.com>

Adds a new option `{cover_excl_apps, Apps}` to exclude apps from coverage
analysis by name.