Add stdlib file name guidelines to CONTRIBUTING (#1026)
Add stdlib file name guidelines to CONTRIBUTING (#1026)

close #1025
cquinn/ponyc,malthe/ponyc,mkfifo/ponyc,jupvfranco/ponyc,mkfifo/ponyc,lukecheeseman/ponyta,cquinn/ponyc,ponylang/ponyc,Theodus/ponyc,jupvfranco/ponyc,Perelandric/ponyc,jemc/ponyc,mkfifo/ponyc,ponylang/ponyc,sgebbie/ponyc,dipinhora/ponyc,Praetonus/ponyc,Theodus/ponyc,malthe/ponyc,malthe/ponyc,jemc/ponyc,cquinn/ponyc,kulibali/ponyc,dipinhora/ponyc,boemmels/ponyc,jupvfranco/ponyc,cquinn/ponyc,sgebbie/ponyc,Perelandric/ponyc,Perelandric/ponyc,boemmels/ponyc,jupvfranco/ponyc,jupvfranco/ponyc,boemmels/ponyc,Perelandric/ponyc,Theodus/ponyc,lukecheeseman/ponyta,mkfifo/ponyc,Praetonus/ponyc,jemc/ponyc,Theodus/ponyc,sgebbie/ponyc,Perelandric/ponyc,Praetonus/ponyc,kulibali/ponyc,malthe/ponyc,mkfifo/ponyc,CausalityLtd/ponyc,sgebbie/ponyc,CausalityLtd/ponyc,dipinhora/ponyc,CausalityLtd/ponyc,Praetonus/ponyc,ponylang/ponyc,boemmels/ponyc,lukecheeseman/ponyta,Theodus/ponyc,sgebbie/ponyc,boemmels/ponyc,kulibali/ponyc,kulibali/ponyc