First release candidate.

Notes:

* some tidbits in the API should be changed to make users and developers
  lives easier, given the cumbersome design of some signatures
* the ertm-cli is fully functional, and the entire API will work with it
* nco configuration is still sketchy: it is not correctly implemented in wrc.bin
* for this to work, a crate with ERTM14/15 module is required, and a USB dongle
  of the specified model (Silicon Labs CP2108) with the approrpiate serial port
  layout (essentially, port 3 is the wrc control console) should be set up