Add effect chaining support with effect1+effect2 syntax

[NickFlach]

Allows running multiple effects in series by specifying them with + separator.

Usage:

# Single effect (unchanged)
./convert echo 0.3 0.3 0.3 0.3 < input.raw > output.raw

# Chained effects (new)
./convert "distortion+chorus+echo" 0.5 0.5 0.5 0.5 < input.raw > output.raw

Supports up to 8 effects in chain. Backward compatible - single effect names still work.

Signed-off-by: The Hand [email protected]