Delete Sessions which cause deserialization errors

Trying to deserialize sessions that are for some reason not
deserializable leads to continous retries at the moment.

As the data is apparently not loadable, it might be a better idea
to remove the data from memcached alltogether in order to avoid
expensive retries.
Create Default Serializer via a Factory method

Thus it is configurable from outside which Serializer and with
which configuration is actually used as default.
Update tomcat 8 to RC10
Add build status icon to README
Merge branch 'compatible_factotory' of github.com:marcust/memcached-session-manager into marcust-compatible_factotory
Rename sys prop to msm.kryo.defaultSerializerFactory
Rename kryo sys prop names *.buffersize.* to *.bufferSize.*

To be a more consistent.

In detail, these are changed:

* msm.kryo.buffersize.initial -> msm.kryo.bufferSize.initial
* msm.kryo.buffersize.max -> msm.kryo.bufferSize.max
Merge branch 'auto_delete' of github.com:marcust/memcached-session-manager into marcust-auto_delete

Conflicts:
	kryo-serializer/src/main/java/de/javakaffee/web/msm/serializer/kryo/KryoTranscoderFactory.java
Let all serializers throw TranscoderDeserializationException on deser errors.