Allow exclusion of Assert conversion

Yosys does support some asserts nowadays. Allowing sv2v to not strip
them out means that you can check formal properties without needing
hierarchical references (which Yosys really doesn't cope well with!)

src/Convert.hs

@@ -55,7 +55,7 @@ phases :: [Job.Exclude] -> [Phase]
 phases excludes =
     [ Convert.AsgnOp.convert
     , Convert.NamedBlock.convert
-    , Convert.Assertion.convert
+    , selectExclude (Job.Assert   , Convert.Assertion.convert)
     , Convert.BlockDecl.convert
     , Convert.DuplicateGenvar.convert
     , selectExclude (Job.Logic    , Convert.Logic.convert)

src/Job.hs

@@ -15,6 +15,7 @@ import System.Environment (getArgs, withArgs)
 
 data Exclude
     = Always
+    | Assert
     | Interface
     | Logic
     | Succinct
@@ -45,7 +46,7 @@ defaultJob = Job
     , siloed = nam_ "siloed" &= help ("Lex input files separately, so"
         ++ " macros from earlier files are not defined in later files")
     , exclude = nam_ "exclude" &= name "E" &= typ "CONV"
-        &= help "Exclude a particular conversion (always, interface, or logic)"
+        &= help "Exclude a particular conversion (always, assert, interface, or logic)"
         &= groupname "Conversion"
     , verbose = nam "verbose" &= help "Retain certain conversion artifacts"
     }