Including the first working version of NagiosWriter.

Conf example:
{ "outputWriters" : [ {
    "@class" : "com.googlecode.jmxtrans.model.output.NagiosWriter",
    "settings" : {
        "typeNames" : [ "name" ],
        "outputFile": "/tmp/denis_jmx",
        "nagiosHost": "HOSTNAME",
        "prefix": "Pre ",
        "posfix": " Pos",
        "filters": ["HeapMemoryUsage_used", "NonHeapMemoryUsage_max"],
        "thresholds": ["@1000000000:3000000000,", ""]
    }
    } ],
    "obj" : "java.lang:type=Memory",
    "resultAlias": "memory",
    "attr" : [ "HeapMemoryUsage", "NonHeapMemoryUsage", "" ]
}

outputFile - Should be the Nagios command file.
    - Cannot be empty.
nagiosHost - The host name defined at Nagios.
    - Cannot be empty.
prefix - Used in the service name to prefix the service description.
    - Can be empty.
posfix - Used in the service name to posfix the service description.
    - Can be empty.
filters - Attr that should be used as a service name.
    -Cannot be empty.
    - Attr HeapMemoryUsage can create 3 outputs:
        - HeapMemoryUsage_used
        - HeapMemoryUsage_min
        - HeapMemoryUsage_max
    For each one that you want to send to Nagios you must include it on filters.
thresholds - It defines the threshold for each filter using the Nagios range definition.
    - Cannot be empty.
    - Syntax:
        - Each threshold has two parts 'warning,critical'
        - Each part can contain a range definition.
            - http://nagiosplug.sourceforge.net/developer-guidelines.html#THRESHOLDFORMAT
        - An empty ("") threshold means always OK.
        - If there is only one field or it starts with comma that service will never be in warning state.
            - "@1000000000"
            - ",@1000000000"
        - If the fields ends with comma that service will never be in critical state:
            - "@1000000000,"

Filters and threholds are bound, so threholds must be in the same position as the filters which it must apply.
Also they must have the same size.
Merge pull request #83 from thuck/master

Including the first working version of NagiosWriter.