Merge branch 'master' into library-use-case

# Conflicts:
#	Cargo.lock
#	Cargo.toml
#	src/bin/scryer-prolog.rs
#	src/loader.pl
#	src/machine/mock_wam.rs
#	src/machine/mod.rs
#	src/machine/system_calls.rs

src/lib.rs

@@ -17,7 +17,8 @@ mod allocator;
 mod arithmetic;
 pub mod codegen;
 mod debray_allocator;
-mod fixtures;
+mod ffi;
+mod variable_records;
 mod forms;
 mod heap_iter;
 pub mod heap_print;