Now works with Tomcat Valves to send access logs

Initial work on Tomcat AccessLog Valve

Put jar-with-dependancies into $CATALINA_HOME/lib/

Add a new Valve into your $CATALINA_BASE/conf/server.xml
``` xml
...
<Valve className="com.stuartwarren.logit.tomcatvalve.ZmqAppender"
               layout="com.stuartwarren.logit.tomcatvalve.Layout"
               socketType="PUSHPULL"
               endpoints="tcp://localhost:2120"
               bindConnect="CONNECT"
               linger="1000"
               sendHWM="1000"
               layoutType="logstashv1"
               iHeaders="Referer,User-Agent"
               oHeaders=""
               cookies=""
               tags="tag1,tag2,tag3"
               fields="field1:value1,field2:value2,field3:value3" />
...
```

Produces logs like:
```
{"message":"GET /?testthing=oeuai HTTP/1.1 304","tags":["tag1","tag2","tag3","valve"],"@timestamp":"2013-10-19T15:47:20.210Z","field3":"value3","field2":"value2","level":"INFO","http":{"request_protocol":"HTTP/1.1","response_headers":{},"request_querystring":"testthing=oeuai","remote_user":null,"request_headers":{"Referer":null,"User-Agent":"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/30.0.1599.69 Safari/537.36"},"response_size":0,"response_status":304,"request_parameters":{"testthing":["oeuai"]},"request_uri":"/","remote_host":"192.168.1.208","request_method":"GET","response_duration":28,"cookies":{}},"hostname":"precise64","field1":"value1","@version":"1","user":"tomcat7"}
```