splice: Script for complex splices

New compiler for splice scripts that parses splice scripts, validates them, converts them to json and back again.

A test is included that puts some advanced and complex scripts into the parser and validates the results that come out.

Changelog-Added: Splice script parser — takes a custom splice query language to bundle multiple complex splices into a single task in a simple way.

common/Makefile

@@ -85,6 +85,7 @@ COMMON_SRC_NOGEN :=				\
 	common/setup.c				\
 	common/shutdown_scriptpubkey.c		\
 	common/sphinx.c				\
+	common/splice_script.c			\
 	common/status.c				\
 	common/status_levels.c			\
 	common/status_wire.c			\