Suggestion: Delete target file when running generate

[nemars]

When generate fails, go is still using old _templ.go files. This makes it easy to miss a problem since build still works and is using out of date generated code. This can be achieved easily by moving targetFileName := strings.TrimSuffix(fileName, ".templ") + "_templ.go" to the begining of generatecmd.compile func and calling os.Remove(targetFileName) before any parsing is done.