Merge pull request #4 from Galvant/dev

Pull from upstream
Initial stab at PyUSB-based instrument.
Initial work on Tektronix DPO 4104.
Merge pull request #5 from Galvant/dev

Added start of usbwrapper. No read functionality yet
Misc. fixes to TekDPO4104 and USBWrapper.
Added instructions to intro.
Initial version of VISA wrapper.
Fixed bugs with VISA wrapping, data loading.
More minor acquisition fixes.
Merge pull request #6 from cgranade/dev

VISA Wrapper, PyUSB wrapper, Tek DPO4104, and bug fixes