Adding noskip task

Demonstrate failing model check by disabling rskip and wskip.

docs/examples/fifo/fifo.sby

@@ -1,7 +1,8 @@
 [tasks]
 prove_oss prove oss
-prove_tabby prove tabby
+noskip prove oss
 cover_oss cover oss
+prove_tabby prove tabby
 cover_tabby cover tabby
 prove_oss cover_oss : default
 
@@ -20,6 +21,7 @@ prove: abc pdr
 [script]
 read -sv fifo.sv
 tabby: read -define USE_VERIFIC=1
+noskip: read -define NOSKIP=1
 read -formal top.sv
 prep -top fifo