Remove gelfv1 Log for now
JSON Serialisation changes

Started work on #67:
Now Using Jackson 2.3.1
Mostly using JSONGenerator rather than ObjectMapper

Log object can now be created with Builder pattern (log4j1)
Simplify custom fields slightly
Added ExampleCustomField to demonstrate Field extension

Made use of Builder pattern in other frameworks
Merge pull request #70 from stuart-warren/next

Next