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
parser main loop: handle unknown sized keywords in a better way
use UNKNOWN as size type for table-like keywords

this allows the parser not to rely on the user-specified table
dimension which is demoted to a semantic check that, produces a
warning in the log if a mistake is detected.