swapped meaning of bounds/layout for linefrags

- bounds is the full size of the line fragment
- layout is the region of the line occupied by text
baseline, layout, & bounds now universal

- all the Text* objects now support bounds/layout queries for the
full-size and used-size respectively
- Text’s x & y can now be accessed through a property called `baseline`
(just like LineFragments)
- `metrics` is now a shorthand for layout.size
off by one (decimal) error
canvas & context units could get out of sync

- setting a non-px size(), running the script, then deleting the size
call and rerunning would create a bitmap at the wrong size for the view
gave Text a better repr
added a max-column-count arg to Text.flow()

- the `columns` arg is the total number of frames you want to have at
the end of the operation (including the Text object’s original frame
- the generator will run `columns`-1 times (i.e., for each *added*
frame)
- calling Text.flow(1) wipes out any previously added frames