This commit handles the conversion of:
* headers
* overviews
* warning_overviews
* controller/view debug output
* errors

where it makes sense

fixes #78

Sexp#line can be used to retrieve or set the line number. No need to
invalidate the hash cache if line is not being set.

when the mass assignment was actually in the controller

instead of losing it and causing all sorts of weird issues
and costing people sleep

although I don't think it makes a difference

where it makes sense

and get a free performance boost, yay!

just like Sexp#line(line)

also fixes issue with sometimes returning hash inside hash