Optional moreLikeThis parameters

Conflicts:
	library/Solarium/QueryType/Select/Result/MoreLikeThis/Result.php

Upgrade to beat the rule of solr ...

Example of "add" with optional update attribute to set a field to null (i.e. delete a field):

<add>
  <doc>
    <field name="employeeId">05991</field>
    <field name="skills" update="set" null="true" />
  </doc>
</add>

Fix proposition for maxScore related notice + unit test (Issue #175)

Added the endpoint property and appropriate accessors to the BufferedAdd plugin and added a call to the get accessor to be passed in to the update() call.