Examples: Improvements to xusb's support for Microsoft OS descriptors

Examples: Improvements to xusb's support for Microsoft OS descriptors

As noted in issue #269, the current xusb implementation does not handle
Microsoft OS descriptors from devices whose vendor code is greater than
0x7F. This commit addresses this limitation by using
libusb_get_string_descriptor() instead of the ASCII variant and parsing
the descriptor separately. Note that this issue was addressed in PR #276,
but that approach was too cryptic to read.

Closes #269, Closes #276

Signed-off-by: Chris Dickens <christopher.a.dickens@gmail.com>