All decoration, particle and module interfaces now takes a
pixman_image_t parameter, and all drawing is done using pixman APIs.
The wayland/xcb backends implement a new interface functions,
get_pixman_image(), that should return a pixman image instance that is
suitable for rendering.
In the wayland backend, the image uses the same backing data as the
cairo surface.
In the XCB backend, we create a new image each time, and then blit it
to the cairo surface at commit time.
In cases where it makes sense, use calloc() instead of malloc():
* When allocating large objects with many members, many for which
NULL/0 is a good default value.
* Arrays etc where we explicitly initialize to NULL anyway.
Since this struct only contained function pointers, make all particles
export those functions directly.
The plugin manager now defines a particle interface struct, and fills
it it by dlsym:ing the functions that used to be in particle_info.
Now that we have a wrapper exposable, we need to implement
on_mouse(). In it, we need to check if we have our own on-click
handler, or else, check if mouse is inside the sub-exposable, or in
the left- or right margin.
This is done by wrapping the selected particle/exposable in a
ramp-specific exposable. This way, we can add the margins before
delegating begin_expose() and expose() to the selected exposable.
This is intended to be a format-like string, with the possibility to
use tag formatters.
The expanded string will later be passed to the system() call.
The ramp particle is configured with a tag name and a list of
particles.
At instantiation time, a single particle is selected from the list,
depending on the tag value and it's minimum and maximum values.
I.e. this particle acts kind of like a progress bar.
