Merge branch 'release/3.1.2'
Fix for issue #183
Merge branch 'develop' of github.com:basdenooijer/solarium into develop
Fix for issue #158
Fix for issue #170
Fix for issue #169
Fix for issue #181
Fix for issue #180
Fix for issue #184
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>
Merge pull request #188 from andrelemos/develop

Upgrade to beat the rule of solr ...
testcases for #188
Replacing relative classes namespaces in PHPDocs by absolute ones to improve IDE support.
Return null explicitely in methods and PHPDoc.
Add a 'use' statement to avoid FQCN in the code.
Improve PHPDocs (adding missing @throws, @return etc).
Fixing bad PHPDocs for methods.
Removed unused lines of codes.
Fix more PHPDocs.
Throw a RuntimeException in case the facet identifier is unknown.