get rid of the 'strict parsing' concept

this is the 'Joakim-style' variant of the patch, i.e., an exception
will always be thrown if an unknown keyword is encountered.
Merge pull request #347 from andlaus/always_parse_strictly

get rid of the 'strict parsing' concept
fix the unit for transmissibility when using the metric unit system

I don't know why exactly this happend, but anyway thanks to [at] bska
for catching it...
Merge pull request #383 from andlaus/fix_metric_transmissibility_unit

fix the unit for transmissibility when using the metric unit system
add default values required to make it possible to terminate keywords early

for many of them the RM says "default is undefined" but that I've come
to the conclusion that this doesn't mean that no default could be
applied, but that the simulator is allowed to screw up if the values
of them are accessed. (Note that in this sense this change is no
change from the current situation, but makes the screw-up more
explicit.)

In particular, note the GRIDUNIT keyword which had some serious JSON
syntax errors in it but so far the unit tests worked anyway for some
reason...
make items which do not have a default un-defaultable

this was a much more common problem than it seemed initially...
make the parsing stage pass even if non-defaultable items have been defaulted

... but throw later when trying to access the data of the item in
question.

Note that this was demanded by [at] joakim-hove and that I do not want
to be held responsible for any issues which are caused by this
approach. (read: please direct your barks to Joakim if you fell on
your nose because of this...)
Revert "add default values required to make it possible to terminate keywords early"

This is not necessary with the "dummy defaults" approach introduced in
the previous patch...