IUS : plusargs makefile variable wasn't getting passed to irun commandline

- running examples/plusargs with SIM=ius didn't show the plusargs defined in
  examples/plusargs/Makefile
examples : making the source of the print/display statements a little clearer

- on my first run through the quickstart guide it wasn't clear to me where
  the statements were coming from in the plusargs test. Making it a little
  more explicit as plusargs is the first test that runs
  when running "make all" from a fresh clone.
Merge pull request #160 from luked80/master

Some examples/plusargs changes.
Issue #161: Add a mixed language example to assist in C work
Issue #161: Failing example when trying to cross language boundary
Issue #161: Add VHDL toplevel for mixed language sims
test post commit hook over https
Issue #143: Add a falling edge trigger
Merge pull request #165 from FinnG/master

Issue #143: Add a falling edge trigger