added basic support for parameters.

[rdaly525]

No description provided.

[leonardt]

This changes the handling of parameters from being represented as key (string), value pairs in a map to being std::pairs of Parameter and Constant.

The changes seem fine, but I'm not exactly sure about the motivation, perhaps this will become more apparent when I review the subsequent PRs?

Mainly, what does having an explicit Parameter provide over having them be keys in a map?

And why use pairs versus a map? Actually, using pairs make sense when iterating for code generation since that's the common pattern (generate the key/value pairs for parameters). This sacrifices parameter lookup performance, but I don't think that will be a common use case (we're interested in building and serializing ASTs, so insertion and pair iteration are priorities), so this change seems okay to me.

So can you provide a simple reason why we need an explicit object versus representing a parameter name as a string?

[rdaly525]

Parameters can be used in the verilog code as literals. We should ideally be able to refer to the same object which is a parameter. If we keep them as strings, we would still need to add the concept of a string as a literal that can be used in expressions.