Added signal clamping in the DSP processor

[anabolyc]

Fixes #136

Issue description:

When DSP settings are enabled with high gain values together with a large volume level, audio starts to fill up with cracking sounds.

This seems to be related to integer overflow when applying gain.

Proposed solution:

Simple integer clamping (to prevent overflow) will replace cracks with clipping, which is always a better choice in terms of resulting sound