Revisit/document use of X-Status-Code in autoConvert metadata

[natevw]

The changes in 747f9e4 fixed #27 but should be reviewed before the release following that.

[natevw]

Also, this needs documentation once it's settled.

[natevw]

Removed the error handling stuff alongside the integration of #35 and bump to 0.10.0.

[natevw]

I think this makes sense, but probably best to migrate this to X-Fermata- prefix instead of just X-.

[natevw]

Or use a Symbol?