Add specification version to the metadata in SigMFCollection (#83)

* add version for collections

---------

Co-authored-by: JKB <j.kuben@era.aero>
Co-authored-by: Kyle A Logue <kyle.a.logue@aero.org>

sigmf/sigmffile.py

@@ -282,7 +282,7 @@ def set_metadata(self, metadata):
         if self.get_global_field(self.NUM_CHANNELS_KEY) is None:
             self.set_global_field(self.NUM_CHANNELS_KEY, 1)
 
-        # set specification version to current implemented version
+        # set version to current implementation
         self.set_global_field(self.VERSION_KEY, __specification__)
 
     def set_global_info(self, new_global):
@@ -758,6 +758,9 @@ def __init__(self, metafiles=None, metadata=None, skip_checksums=False):
         else:
             self.set_streams(metafiles)
 
+        # set version to current implementation
+        self.set_collection_field(self.VERSION_KEY, __specification__)
+
         if not self.skip_checksums:
             self.verify_stream_hashes()