improve flowspec support

[xiaopeng163]

issue #52

now flowspec support message like:

{
    "attr":{
        "1": 0, 
        "2": [], 
        "5": 100, 
        "14": {
            "afi_safi": [1, 133], 
            "nexthop": "", 
            "nlri": [
            	{"1": "192.88.2.3/24", "2": "192.89.1.3/24", "3":"=17|=80|>=8000"},
            	{"1": "192.77.2.3/24", "2": "192.77.1.3/24", "5": "=80|=8080"}]
        },
        "16":[[32774, "100:6250000"]]
    }
}

filter value support =, <,>,>=,<=, and |

[coveralls]

Coverage increased (+0.002%) to 60.655% when pulling c22e859 on xiaopeng163:master into 433c034 on smartbgp:master.