all: replace "Debug" with "AssetDebug"

Josh Bleecher Snyder made the point that if this file is compiled
in with other files in a package, "Debug" is a very generic word.
"AssetDebug" is less likely to have conflicts with existing packages.

This is a breaking change, which I'm not happy about, but it's a new
one, so hopefully very few people are relying on the behavior that was
recently added. Add a "CHANGELOG" to helpfully make this change more
clear to people.

Author: kevinburke

CHANGELOG.md

@@ -0,0 +1,8 @@
+## 3.21.0
+
+Replace "Debug" with "AssetDebug" to reduce the likelihood of conflicts.
+
+## 3.20.0
+
+Add the "Debug" constant if assets have been generated using the `--debug` flag
+at the command line.

convert.go

@@ -96,8 +96,8 @@ func Translate(c *Config) error {
 	if err := writeTOC(buf, toc); err != nil {
 		return err
 	}
-	_, err = fmt.Fprintf(buf, `// Debug is true if the assets were built with the debug flag enabled.
-const Debug = %t
+	_, err = fmt.Fprintf(buf, `// AssetDebug is true if the assets were built with the debug flag enabled.
+const AssetDebug = %t
 
 `, c.Debug)
 	if err != nil {