Fix Key_StringToKeynum to return lowercased ascii

Fixes bind and unbind uppercase ascii and uppercase ascii in cl_consoleKeys.

keycodes.h states "normal keys should be passed as lowercased ascii"
Show lowercased ascii in bind command
Rewrite comment for CG_VOIP_STRING
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'