alsamixer: added configuration file parser

alsamixer: added configuration file parser

Added configparser.c and curskey.c:
  - Lines starting with arbitrary whitespace + '#' are comments
  - Words in a command name don't have a fixed order (toggle_mute is the
      same as mute_toggle)

Moved read_file() from textbox.c to utils.c, so configparser.c can make
use of it.

Added command line options:
  -f/-F to specify/disable configuration file
  -m/-M to enable/disable mouse

Signed-off-by: Benjamin Abendroth <braph93@gmx.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>