"c" now also does manchester decoding

[jeffguy]

My SDR instructor said manchester encoding is very widely used and he thinks lots of people would be grateful if dspectrum supported it. So, if you like, this patch adds that support.

I don't know Ruby, so there's probably a cleaner way to do this.

[tresacton]

Hi Jeff,

DSpectrum has been superseded by DSpectrumGUI. Your instructor is quite right, Manchester is pretty widely used, particularly by RKE systems. DSpectrumGUI supports Manchester (in both common formats) and PWM. I appreciate you taking the time to submit this PR. I hope you take a look at DSpectrumGUI at some stage, and hopefully contribute there =)

Cheers,

nullwolf