hoaparse: make it possible to read from a string

* src/hoaparse/public.hh, src/hoaparse/parsedecl.hh,
src/hoaparse/hoascan.ll, src/hoaparse/hoaparse.yy: Implement this new
interface.
* wrap/python/spot.py (automata): Use it when the argument contains
a newline.
* wrap/python/tests/automata-io.ipynb: Test it.

src/hoaparse/hoascan.ll

@@ -390,6 +390,14 @@ namespace spot
     return 0;
   }
 
+  int
+  hoayystring(const char* data)
+  {
+    yy_scan_string(data);
+    hoayyreset();
+    return 0;
+  }
+
   int
   hoayyopen(int fd)
   {