changed USB transfer sizes and baud rate for FTD2XX implementation

- set USB transfer size to 2x default value
- set baud rate to default value (9600)
- if errors occur: throw exception to clearly indicate the problem
- added a few descriptive comments
- attempt at addressing psi46/pxar#121

(cherry picked from commit a058323e7165de2a41dd8c07ed64c93ae0ecc19b)