Update CCPP tech doc: pointer variables are not allowed in CCPP-compliant parameterizations

[climbfuji]

Description

We've determined that CCPP will not support pointer variables in CCPP-compliant parameterizations, so let's add this information to the CCPP technical documentation.

[mkavulich]

@climbfuji I'm in the process of updating the Technical Documentation now. Just to clarify, internal pointers within physics schemes will still be allowed, right? They will just not be supported as CCPP-compliant variables passed between schemes/hosts?

[climbfuji]

@climbfuji I'm in the process of updating the Technical Documentation now. Just to clarify, internal pointers within physics schemes will still be allowed, right? They will just not be supported as CCPP-compliant variables passed between schemes/hosts?

Yes, as far as I remember this is correct.

[mkavulich]

Another note here while I'm wrapping my head around things: I noticed all of the framework code for dealing with pointers is still present (for example, the "pointer" attribute added in #552) as well as unit tests. I assume these will be removed in the future?

I added wording here and here that I think properly captures the current state of things, let me know what you think.