switched to Swift Package, and other improvements

Author: bretsko

.gitignore

@@ -1,18 +1,5 @@
 .DS_Store
-build/
-*.pbxuser
-!default.pbxuser
-*.mode1v3
-!default.mode1v3
-*.mode2v3
-!default.mode2v3
-*.perspectivev3
-!default.perspectivev3
-*.xcworkspace
-!default.xcworkspace
-xcuserdata
-profile
-*.moved-aside
-DerivedData
-.idea/
-*.xcuserstate
+/.build
+/Packages
+/*.xcodeproj
+xcuserdata/