warnings: enable quiet builds
Merge pull request #93

5362875 warnings: enable quiet builds (Cory Fields)
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)
Implementations for scalar without data-dependent branches.
Use Montgomery multiplication for scalar inverses.
Some simplications in the muladd sequences