Rename line_trace() to trace()

[tancheng]

Now all the modules come with line_trace() to provide trace information. We might want to change it to trace() to make it conformed with construct() and place().

[cbatten]

I like the idea of calling in trace(). Can you see what Shunning thinks?

[cbatten]

@jsn1993 what do you think about renaming line_trace() to just be trace()? That way construct(), place(), and trace() are all verbs ... in general classes should be nouns and methods should be verbs ... so my vote would be to use trace().