XMLParser now builds a list of leafnodes

- stores the location and selector for each tag
- new offset arg sets the character offset (to the prior length of the
Text that’s being appended to) which adjusts the saved tag locations
dropped old module init
return baseline as a Point rather than offset
line() now supports relative x/y distances

- calling line() with an x/y positional coord (or Point) and a `dx` or
`dy` kwarg will draw a line relative to the initial point – e.g.,
line(25,25, dy=50) will draw a line from (25, 25) to (25, 75)
the whole brevity thing