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
explicitly set USB transfer sizes and baud rate for libftdi implementation

- set USB transfer size to default value (4096)
- set baud rate to default value (9600)
- added a few descriptive comments
- attempt at addressing psi46/pxar#121
Merge branch 'master' of https://github.com/psi46/pxar
Merge branch 'master' of https://github.com/psi46/pxar