Added prefix flag, and updated file name output. Changed parser

package's ParsePackage to take prefix and updated related skip
conditional.  Also updated args in call to ParsePackage within
server. Last paragraph of main package comment was updated, along
with the second to last paragraph of readme.

jsonenums.go

@@ -58,9 +58,10 @@
 // or a set of Go source files that represent a single Go package.
 //
 // The -type flag accepts a comma-separated list of types so a single run can
-// generate methods for multiple types. The default output file is t_string.go,
-// where t is the lower-cased name of the first type listed. The suffix can be
-// overridden with the -suffix flag.
+// generate methods for multiple types. The default output file is
+// t_jsonenums.go, where t is the lower-cased name of the first type listed.
+// The suffix can be overridden with the -suffix flag and a prefix may be added
+// with the -prefix flag.
 //
 package main
 
@@ -79,6 +80,7 @@ import (
 
 var (
 	typeNames    = flag.String("type", "", "comma-separated list of type names; must be set")
+	outputPrefix = flag.String("prefix", "", "prefix to be added to the output file")
 	outputSuffix = flag.String("suffix", "_jsonenums", "suffix to be added to the output file")
 )
 
@@ -97,7 +99,7 @@ func main() {
 		log.Fatalf("only one directory at a time")
 	}
 
-	pkg, err := parser.ParsePackage(dir, *outputSuffix+".go")
+	pkg, err := parser.ParsePackage(dir, *outputPrefix, *outputSuffix+".go")
 	if err != nil {
 		log.Fatalf("parsing package: %v", err)
 	}
@@ -134,7 +136,8 @@ func main() {
 			src = buf.Bytes()
 		}
 
-		output := strings.ToLower(typeName + *outputSuffix + ".go")
+		output := strings.ToLower(*outputPrefix + typeName +
+			*outputSuffix + ".go")
 		outputPath := filepath.Join(dir, output)
 		if err := ioutil.WriteFile(outputPath, src, 0644); err != nil {
 			log.Fatalf("writing output: %s", err)