Fix all linter errors

- Add explicit error ignoring with _ = for Close/Remove calls
- Rename WriteTo to Write to avoid io.WriterTo interface conflict
- Fix errcheck warnings in fetch, freshen, gen, mfer, checker,
  deserialize, serialize, and output files

internal/cli/mfer.go

@@ -41,7 +41,7 @@ const banner = `
     \__\/         \__\/       \__\/         \__\/`
 
 func (mfa *CLIApp) printBanner() {
-	fmt.Fprintln(mfa.Stdout, banner)
+	_, _ = fmt.Fprintln(mfa.Stdout, banner)
 }
 
 // VersionString returns the version and git revision formatted for display.
@@ -201,7 +201,7 @@ func (mfa *CLIApp) run(args []string) {
 				Name:  "version",
 				Usage: "Show version",
 				Action: func(c *cli.Context) error {
-					fmt.Fprintln(mfa.Stdout, mfa.VersionString())
+					_, _ = fmt.Fprintln(mfa.Stdout, mfa.VersionString())
 					return nil
 				},
 			},