remove redundencies in the Doxygen documentation.

really portable, and Visual Studio complains when they are not explicitely
    cast.

environment variables handling. Replaced that with three per-bitmap
    functions: cucul_set_bitmap_antialias(), cucul_set_bitmap_color() and
    cucul_set_bitmap_dithering().
  * Added cucul_set_bitmap_brightness() and cucul_set_bitmap_contrast()
    prototypes (but did not implement them yet).
  * Added cucul_set_bitmap_charset() to choose what characters are going
    to be used for the bitmap rendering.
  * Removed the now useless cucul_get_feature(), cucul_set_feature() etc.

can add new exporters without changing the API.

raw driver. I know it is inconsistent to have the loader in libcucul
    and the exporter in libcaca but I'll find a way to harmonise that.

canvas size (use cucul_init(0, 0) for the old behaviour).

* Got rid of static buffers; we now use cucul_free() to free exported
    buffers.
  * Fixed light background in the ANSI exporter by adding escape sequences for
    most terminal emulators.

as multiboot kernels.

and simplified the handle_resize() API. Still can be polished.

documentation to explain this behaviour.

properly credited authors and documented a few things.

now because we only do ASCII, but that will let us do Unicode later.

* Renamed caca_refresh() into caca_display() which makes more sense.
  * Optimised gl_bgpal by directly storing floats instead of doing the
    conversion at runtime.
  * Handle resizing in cucul_set_size() and try to keep as much information
    as possible from the previous canvas.
  * Moved most global variables into cucul_t or caca_t contexts.
  * Moved time.c into libcaca.

of unicode letters) is now separated from the higher level rendering and I/O
(that is, libcaca). This commit totally breaks the API, but once everything
is polished I will think about source-level backward compatibility. Most
drivers are broken, but X11 still sorta works.

  The new design is much more object-oriented and allows having several
active renderers at the same time, changing renderers on the fly, and more
important, having no renderer at all (useful for converters, or when you
want to do your own renderer).

  And in case you are still wondering, the libcucul acronym has "Unicode"
because I want to support at least a subset of Unicode. There are awesome
glyphs in it, including the ones inherited from Codepage 437 such as
"gray 25%" that are used in DOS and Win32 ANSI art.