acc: introduce acc_cond::name()

* spot/twa/acc.cc, spot/twa/acc.hh (acc_cond::name): New method.
* spot/twaalgos/dot.cc: Use it.
* tests/python/acc_cond.ipynb: Add a small test.
* NEWS: Mention it.

tests/python/acc_cond.ipynb

@@ -15,7 +15,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.5.4"
+   "version": "3.6.3"
   },
   "name": ""
  },
@@ -1266,6 +1266,36 @@
      ],
      "prompt_number": 46
     },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "If the acceptance condition has some known name, it can be retrieved using the `name()` method.  By default the name given is a human-readable string close that used in the HOA format, but with proper accents, and support for name like `Streett-like` or `Rabin-like`.  The argument `arg` can specify a different style using the same syntax as in `--format='%[arg]g'` when using the command-line tools."
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "print(acc.name())\n",
+      "print(acc.name(\"d\"))  # <- Style used by print_dot(aut, \"a\")\n",
+      "print(acc.name(\"0\"))  # <- no parameters"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "generalized-B\u00fcchi 4\n",
+        "gen. B\u00fcchi 4\n",
+        "generalized-Buchi\n"
+       ]
+      }
+     ],
+     "prompt_number": 47
+    },
     {
      "cell_type": "markdown",
      "metadata": {},
@@ -1293,7 +1323,7 @@
        ]
       }
      ],
-     "prompt_number": 47
+     "prompt_number": 48
     },
     {
      "cell_type": "markdown",
@@ -1314,13 +1344,13 @@
       {
        "metadata": {},
        "output_type": "pyout",
-       "prompt_number": 48,
+       "prompt_number": 49,
        "text": [
         "{0,1,2,3}"
        ]
       }
      ],
-     "prompt_number": 48
+     "prompt_number": 49
     },
     {
      "cell_type": "markdown",
@@ -1351,7 +1381,7 @@
        ]
       }
      ],
-     "prompt_number": 49
+     "prompt_number": 50
     },
     {
      "cell_type": "markdown",
@@ -1381,7 +1411,7 @@
        ]
       }
      ],
-     "prompt_number": 50
+     "prompt_number": 51
     },
     {
      "cell_type": "code",
@@ -1403,7 +1433,7 @@
        ]
       }
      ],
-     "prompt_number": 51
+     "prompt_number": 52
     },
     {
      "cell_type": "code",
@@ -1425,7 +1455,7 @@
        ]
       }
      ],
-     "prompt_number": 52
+     "prompt_number": 53
     }
    ],
    "metadata": {}