Address 'constant-time' TODOs in field impls
Merge pull request #92

137e77a Address 'constant-time' TODOs in field impls (Peter Dettman)
Fix typo
Label variable-time functions correctly and don't use those in sign
Merge pull request #94

da55986 Label variable-time functions correctly and don't use those in sign (Pieter Wuille)