Add Speaker Softness Control

[trudnai]

Adjusting fadeLevel increments in spkr_toggle() makes it possible to change softness of sound. Softer sound might give you better audio for speech synthesis, also some people might prefer that.
Harder sound might give you more accurate sound on average games.

• Hard: fadeLevel *= 0.16; or below
• Medium: fadeLevel *= 0.64;
• Soft: fadeLevel *= 0.75; or above