Use VS 2019 on appveyor, update scons
Use VS 2019 on appveyor, update scons

ghewgill/neon-lang,ghewgill/neon-lang,ghewgill/neon-lang,ghewgill/neon-lang,ghewgill/neon-lang,ghewgill/neon-lang,ghewgill/neon-lang,ghewgill/neon-lang,ghewgill/neon-lang,ghewgill/neon-lang