sealed types development moved to new branch sealed-types

[Vicente Romero]

Hi all,

I have closed branch records-and-sealed after cherry-picking the sealed 
code from there. Please continue any new development in the 
`sealed-types` branch. I have tried to get all the working bits, but if 
anyone notice something missing please chime in. The old 
records-and-sealed branch have some patterns code that could be useful 
in the future but that doesn't make sense for a sealed only repo so it 
was left behind.

Thanks,
Vicente