- add unified frontend configuration record to make adding future
  options easier
- use ExceptT throughout, rather than using runExceptT at internal
  boundaries

Workarounds for resolved iverilog issues have been removed.

- upgrade to happy 1.20
- placate GHC warning on version fallback
- fix stack sdist failure

- support ports with sizes which depend on constant functions
- restore package item injection utility to package conversion module
- additional unbased unsized conversion test coverage

- references to other instances are no longer flagged
- special handling for genvars to avoid flagging and modport scoping
- interface inlining visits expressions in declarations
- Scoper has interface for removing entries

- don't keep unused template modules even if they are fully-specified
- don't reduce modules with unbound type parameters

The interface conversion no longer substitutes parameters immediately,
instead fully scoping modports and allowing hierarchical constants to be
resolved separately. This fixes an issue where struct parameters could
lose their type information during substitution. The conversion also now
handles renaming references to the module or interface top-level scope.

- scoper item injection can no longer affect generate scoping
- cast conversion injects functions into the top level when possible
- cast conversion considers loop variables to be local
- `else if` generate blocks are still scopes at the current level

- updated representation and added codegen for sequence match items
- fix incorrect codegen for `iff` property expression

- moved 4 phases to initial set and 3 to final set
- fix synthetic unnamed genblocks preventing name resolution
- asgnop conversion folds in unisub when possible

- substitute enum item values directly into usage sites rather than
  creating synthetic localparams
- substitution handles shadowing of expressions in enum item values
- disconnected scopes can reference conflicting enum items

- convert loops with no or many incrementations
- restrict AST node to only contain traditional initializations
- parser elaborates for loop decls into a synthetic block
- decl list codegen is now specific to parameter decl lists
- update jump conversion special cases for new representation
- first experiments with bimapM

- don't evaluate AST after procedural assignment collection
- don't use State monad during rewrite
- use Writer rather than State for procedural assignment collection
- use Scoper access generation shortcut utility
- cleanup as-patterns and legacy logic

- don't evaluate AST after depth collection
- don't use State monad during rewrite
- add Scoper utility for generating accesses without inserting element
- cleanup as-patterns and unnecessary verbosity