docs/devices/t650: add reprogrammable keys
docs/devices/m525: add ltunify and solaar output
docs/logitech: Add DJ receiver spec

docx files is taken from hidpp20 public folder[1] and was converted to
PDF format using:

    loffice --convert-to pdf ...docx
    qpdf --linearize orig.pdf ...pdf

Mirrored on https://lekensteyn.nl/files/logitech/.

 [1]: https://drive.google.com/#folders/0BxbRzx7vEV7eWmgwazJ3NUFfQ28
docs/devices: add K750 (from Julien Danjou)

Received from Julien Danjou on the devkit mailing list.
Merge pull request #121 from Lekensteyn/doc-updates

Documentation updates: DJ pdf and devices