split into lib and bin

* makes most pub things in src/ pub(crate) as not to expose things accidentally
  * only those things needed by src/bin/scryer-prolog.rs and tests/scryer.rs
    should be pub
* split src/main.rs into src/lib.rs and src/bin/scryer-prolog.rs
* add tests folder and run most of the files in src/tests with cargo test
  added bytes method to Stream in src/machine/streams.rs to check if stdout is as expected

src/lib.rs

@@ -0,0 +1,35 @@
+#[cfg(feature = "num-rug-adapter")]
+use num_rug_adapter as rug;
+#[cfg(feature = "rug")]
+use rug;
+
+#[macro_use]
+mod macros;
+mod allocator;
+mod arithmetic;
+mod clause_types;
+mod codegen;
+mod debray_allocator;
+mod fixtures;
+mod forms;
+mod heap_iter;
+mod heap_print;
+mod indexing;
+mod instructions;
+mod iterators;
+pub mod machine;
+pub mod read;
+mod targets;
+mod write;
+
+use machine::*;
+
+use nix::sys::signal;
+use std::sync::atomic::Ordering;
+
+pub extern "C" fn handle_sigint(signal: libc::c_int) {
+    let signal = signal::Signal::from_c_int(signal).unwrap();
+    if signal == signal::Signal::SIGINT {
+        INTERRUPT.store(true, Ordering::Relaxed);
+    }
+}