-incval
template: pers?clnt=<name|pass>&com=incval&usr=<usr>&<ftr_1>=<step_1>&...<log>
          Order of query params is not important: updates of feature
          values are performed in the order they appear in the request,
          however the changes are of accummulative nature, so the final
          result is the same.
descript: for the specified user, the value for each specified feature
          is increased by x (decreased if x is negative), where x is
          the step corresponding to that feature. Rows with string
          values that cannot be converted to numeric, are not affected.
          If no matches are found, or if all matches have values that
          cannot be converted to numeric, no records will be updated
          (200 OK will still be returned). If any <step_i> parameter
          cannot be converted to numeric, 401 is returned. If the error
          code 401 is returned then no updates have taken place in the DB.
          If the log parameter is been used then the transaction will be loged 
          into the num data table
example : pers?clnt=name|pass&com=incval&usr=kostas&lang.gr=1&expert=-0.34
returns : 200 OK, 401 (fail, request error), 501 (fail, server error)
200 OK  : in this case the response body is as follows
          <?xml version="1.0"?>
          <?xml-stylesheet type="text/xsl" href="/resp_xsl/rows.xsl"?>
          <result>
          <row><num_of_rows>number of relevant rows</num_of_rows></row>
          </result>
comments: the reference to the xsl file allows to view results
          in a web browser. In case the response body is handled
          directly by an application and not by a browser, this
          reference to xsl can be ignored.