Write a synthetic document about IQ demodulation / Hilbert transform

[Aurelie-Mutschler]

Gather information about IQ demodulation / Hilbert transform.

Indicative due date : June 1st, 2017

Criteria to close the issue :

• fork the repo
• edit literature.bib with your references (.bib files can be handled for example with bibDesk on macOsX)
• edit the file references/sigproc/envelope_extraction.md with a summary of your findings. In this file you'll be able to cite references from literature.bib by calling : {{ "some-key" | cite }} where some-key has to be replaced by the cite key from literature.bib (you can inspire yourself from references/sigproc/IMGQ_metrics.md to understand how citations work)
• make a pull request refering to this issue

[Aurelie-Mutschler]

thanks @Halipster still some bugs with the katex plugin, the equations in simple $ don't seem to be parsed waiting for updates to close the issue

[Aurelie-Mutschler]

thanks @halipster I handled the bugs with katex