Add Text To Speech To A Garmin C510/530 GPS

[josh] pointed out this hack for Garmin C510 and C530 GPS units. The newer C550 and C580’s feature text to speech directions. [Phil Hornby] put together a walk through that will add this valuable feature to the older units. He took advantage of the firmware similarities of the various Garmin units and got it working. The hack requires some compromises due to memory constraints, but it’s pretty straight forward.