* Fix cucul_utf32_to_cp437() call in the VGA output.

and return a value.

in all .c files that needed it.

their name, eg. cucul_create() -> cucul_create_canvas() etc.
  * Moved buffer-related functions to cucul/buffer.c.

* Renamed canvas handle variables from "c" to "cv". Eh ouais mon gros.

such as cucul_dither_t instead of struct cucul_dither.
  * Made cucul_buffer_t an opaque structure and implemented the two getters
    cucul_get_buffer_data() and cucul_get_buffer_size().
  * Documented all missing functions and function parameters.

remove redundencies in the Doxygen documentation.

that we have one function less.
  * Fixed coding style.
  * Removed FUCKING TABS.               ____.------.___
                           _______.----'`` ``` `` ``` ``-.
                      _.--' ` ```` ` `  ` ```  ``    ``  ``.
                  _.-'    ' ` `` ```      `` ` `'           `.  _
               .-''      ` H A H A H A `'  M A I S            \/.)
     .    . .-' /       `         `                  `      `` ||
     |`-.(``-.          `      `       `        ' `  `    ```  |\
     `.  '\```\        ``   `     V I E U X   ' ' ``  `-``    -|\\
       `/''````)       `` `          -        -   `````  ' '.' |\_)
        |`'_._`       ```      ''`  P O R C .   . ````        /
        // @) \    `   ``       ''' .              ```      '/
       /''''' |     ` \).`.'-.  ''' _    _         .`` `   '/
     .''''- `-'`.   . //   )--   '/,,',,' ,,,,''__,._`' '  /
   .'    ` `-  `   ' .'   /   ' /,;;;, ,___.---'     \ '' / \
   (`.  .'` __',`''''.--'/   ' /'-----'              | ' /  ))
    `'-'/  `'''_.---' \;;|-  '/            ,,,       | ''|`- |
      `'--'---'        |;|   /   ,,,,;;;;;;;;;;,,,,, |-' /`  |
                       |;|-'|   ,;;;;;;;;;;;;;;;; ;;;/  /|`'''
                       ''',,,''',,,,,,,,,,,,,,,'    /,,'''
                                   ''''

* Cosmetic code changes.

80x25 upon initialisation.