Adding and joining paths

The result of this example looks the same as the [''pathitem''
../drawing/pathitem.html] example from the ''Basic drawing'' section. However, we
are using a different approach to construct the paths in this example: we add
and join paths. ... When ''adding'' two paths, the resulting path just contains
all the subpaths from the first and the second path as its subpaths. The
''join'' operation between two paths is similar but it combines the last
subpath from the first path and continues it by the first subpath of the second
path. Thus, ''join'' does not increase the number of subpaths like the ''add''
operation.

! A similar result in terms of the line thickness could be achieved by setting a
different scale for the linewidth by

    unit.set(wscale=10)

immediately after the import statement. The unit system of PyX is aware of
several length types (unscaleable ''true'' coordinates `t`, regular ''user'' coordinates
`u`, ''visual'' coordinates `v` for arrows, symbols and other small visual components,
line ''widths'' `w` and the ``text`` sizes `x`). The length types can be scaled
independent of each other (except for ''true'' coordinates, which cannot be scaled at all).

! Note that joining two paths might insert a line connecting the first and the
second path. For example, we could skip the second line when constructing
`rect2` in our example above without any change in the result.
