Is metadata well exported

[Ducasse]

teh following leads to an error

| doc exporter |
doc := MicrodownParser parse: '

{ 
"author" : "stf" 
}

# foo 

bar '.
doc metaDataElement atKey: #lastModificationDate put: Date today printString.
exporter := MicTextualMicrodownExporter new.
exporter visit: doc.
'foo.md' asFileReference writeStreamDo: [ :s | s nextPutAll: exporter contents] 

[Ducasse]

We should check this.