Interim but working support for crunched data streams when reading from the

device; writes haven't been converted yet. Reduces the bandiwidth from about
800kB/s to about 500kB/s, which is about what I thought.

tests/crunch.cc

@@ -0,0 +1,43 @@
+#include "globals.h"
+#include "bytes.h"
+#include "crunch.h"
+
+static uint8_t outputbuffer[64];
+
+static void test_crunch()
+{
+    crunch_state_t cs = {};
+    Bytes inputdata = { 0x01, 0x7f, 0x80, 0x81, 0x01 };
+    cs.inputptr = inputdata.begin();
+    cs.inputlen = inputdata.size();
+    cs.outputptr = outputbuffer;
+    cs.outputlen = 64;
+    crunch(&cs);
+    donecrunch(&cs);
+    Bytes outputdata(outputbuffer, cs.outputptr - outputbuffer);
+
+    assert((outputdata == Bytes{ 0x01, 0x7f, 0xb0, 0x10 }));
+}
+
+static void test_uncrunch()
+{
+    crunch_state_t cs = {};
+    Bytes inputdata = { 0x01, 0x7f, 0xb0, 0x10 };
+    cs.inputptr = inputdata.begin();
+    cs.inputlen = inputdata.size();
+    cs.outputptr = outputbuffer;
+    cs.outputlen = 64;
+    uncrunch(&cs);
+    doneuncrunch(&cs);
+    Bytes outputdata(outputbuffer, cs.outputptr - outputbuffer);
+
+    assert((outputdata == Bytes { 0x01, 0x7f, 0x80, 0x81, 0x01 }));
+}
+
+int main(int argc, const char* argv[])
+{
+    test_crunch();
+    test_uncrunch();
+    return 0;
+}
+