Implement PUS Services 20 and 12

[andreadimax]

Fantastic project! Love to see Rust in aerospace!

Could be very useful a module implementing PUS service 20 for monitoring parameters and another one for Service 12.

Hope to see this software in a future ESA mission 😄

[robamu]

We used S20 for parameters. I had a brief glance at the PUS standard again:

• The parameter ID is was tailored to the use-case of missions, consisting of a domain ID, unique ID and row/column ID to allow access to vector/matrix parameters for our tailored service implementation
• The standard looks tailored towards parameter storage in raw memory or RAM. nowadays, parameter storage in files
  is also common

Might be worthwhile to provide a service 20 conversion layer tailored towards our use-case.

I never did much with the PUS service 12, would have to look at that as well.

[andreadimax]

What are your future works? Do you accept contributions?

[robamu]

Yes :)