Comments on types correctly have single newlines stripped from them, but comments on fields do not. This is because of the behavior described in the documentation for ExtractGoComments:
When parsing type comments, we use the go/doc's Synopsis method to extract the first phrase only. Field comments, which tend to be much shorter, will include everything.
Synopsis is also the mechanism by which unmeaningful newlines are stripped, so we also lose this behavior for fields.
Related to (but not solved by) #67.