Fix Internal DAC

[ferbar]

I had to do some changes for my project:

• Internal DAC - esp32 internal DAC wants unsigned data,
• fix some cracking - increased buffer size, changed file format to 'raw' in documentation because the aiff header adds cracking if it is not removed in the code
• removed some pointers

unfortunately I don't have a i2s DAC, so these changes are only tested with the internal DAC