Should not escape when target is link format or file format.

Now, content of F< ... > notation and L< ... > notation is escaped.

__e.g.__
F\<.dot_file\> => `.dot\_file`
L\<foo_link\> => \[foo\_link\](http://search.cpan.org/perldoc?foo\_link)

I think, they should not be escaped.
So I fix it. Could you review and merge this?