CODE_OWNERS: Add GitHub accounts, for PR tagging purposes

CODE_OWNERS.TXT

@@ -4,49 +4,60 @@ They are also the gatekeepers for their part of Swift, with the final word on
 what goes in or not.
 
 The list is sorted by surname and formatted to allow easy grepping and
-beautification by scripts.  The fields are: name (N), email (E), web-address
-(W), description (D).
+beautification by scripts.  The fields are: name (N), email (E),
+GitHub account (G), description (D).
 
 N: Ben Cohen
 E: [email protected]
+G: airspeedswift
 D: Swift standard library
 
 N: Erik Eckstein
 E: [email protected]
+G: eeckstein
 D: SILOptimizer
 
 N: Xi Ge
 E: [email protected]
+G: nkcsgexi
 D: Markup, Migrator, lib/Syntax
 
 N: Doug Gregor
 E: [email protected]
+G: DougGregor
 D: AST, Basic, Parse, Sema
 
 N: Joe Groff
 E: [email protected]
+G: jckarter
 D: SIL, SILGen, everything in Swift not covered by someone else
 
 N: Argyrios Kyrzidis
 E: [email protected]
+G: akyrtzi
 D: IDE, SourceKit, swift-ide-test
 
 N: Luke Larson
 E: [email protected]
+G: lplarson
 D: Swift Benchmark Suite
 
 N: John McCall
 E: [email protected]
+G: rjmccall
 D: Demangler, IRGen, Runtime
 
 N: Slava Pestov
 E: [email protected]
+G: slavapestov
 D: Reflection, SwiftRemoteMirror
 
 N: Jordan Rose
 E: [email protected]
+G: jrose-apple
 D: ClangImporter, Serialization, (Objective-)C printer, Driver
 
 N: Anna Zaks
 E: [email protected]
+G: AnnaZaks
 D: SIL diagnostics passes