[feature] modified validateKnowRows of MetadataValidator trait to check for PermitEmpty global directive
[feature] added new global directive PermitEmpty to allow empty CSV files
[feature] added new permitEmptyDirective to global directives definition and renumbered parsers
[testsuite] added new tests and modified existing to test application of PermitEmpty global directive under various conditions
[testsuite] added new tests for detection of @permitEmpty global directive
[ignore] improving comments in validateKnowRows method of MetadataValidator trait
Merge pull request #63 from rwalpole/master

added global directive to permit empty files