Point objects now support +/- operators
Text.glyphs & .lines provide finer-grained metrics

- the .glyphs property can be subscripted based on character indices
(or a slice of them). It returns one or more LineFragment tuples
describing all the lines in the range
- the .lines property can be subscripted using line indices and its
fragments describe the entire run of text per-line
- line fragment tuples provide bounding boxes for the total and ‘used’
portions of the line as well as the characters displayed and their
baseline offset