usb: squashed thread related changes
uhd: packet handler minor changes

* overflow recovery also in case of alignment failure
* print D (discontinuities) instead of O in seq errors
uhd: dont handle multi-chan overflow recovery here
uhd: update the docs for the D discontinuity indication
b100: moved usb wrapper class into b100 impl

* since its only used internally in b100
uhd: squashed support modules for usrp3 fpga cores
b100: call demuxer realloc sid
usb: added logging capability w/ env var
b200: squashed support for b200 onto master branch
b200: added eeprom map needed for last commit
b200: skeleton documentation rst manual
b200: use existing query rate calls to clip