Dynamic log event

I think this patch need a bumb in the minor version number. 

The changes I've made is:
* Removed the `LogEvent`, a dynamic object is used instead
* Changed example mapping to use lower case since that is the default if you don't have metadata on the object you index, which doesn't exist on the dynamic object
* Fixed the use of properties in log4net so it is now possible to add properties to the `GlobalContext`, `ThreadContext`, `LogicalThreadContext` or the `LoggingEvent` and they will be added to the indexed object.
* Added test to verify it works to add to properties.

On a side note, I don't think the bat script and sample mapping is needed since it will create default indexing as a start and that is probably good for most of the cases.