Get at least basic elaboration of analog processes and contribution statements. Bring the statements and analog statements together and net future elaboration work sort out which statements are valid in a given context. This makes sense because there really is a lot of syntactic overlap, and analog behavioral code is processed somewhat sequentially.
Contribution statements have an l-value and r-value. Parse those expressions into pform so that elaboration has something to work with. In this process, this patch also changes the PECallFunction class to use the vector template instead of the svector template. The latter doesn't add anything over the STL vector template, so this is a start of working the svector out.
Organize the parsing infrastructure for parsing analog processes, including holding them in scopes, and collecting analog statements.