move OS commands into their own package

pkg/commands/oscommands/os_default_platform.go

@@ -0,0 +1,20 @@
+// +build !windows
+
+package oscommands
+
+import (
+	"runtime"
+)
+
+func getPlatform() *Platform {
+	return &Platform{
+		OS:                   runtime.GOOS,
+		CatCmd:               "cat",
+		Shell:                "bash",
+		ShellArg:             "-c",
+		EscapedQuote:         "'",
+		OpenCommand:          "open {{filename}}",
+		OpenLinkCommand:      "open {{link}}",
+		FallbackEscapedQuote: "\"",
+	}
+}