Log Message:
(math/R-emdbook) Updated 1.3.12 to 1.3.13

Changes in version 1.3.13:

        * various cleanup (CITATION file, junk test directory, old
          URLs, etc.)

        * 'deltamethod': attempt to improve handling of functions
          missing from derivs table when warning language is not
          English

        * 'lambertW': slightly improved reporting when iteration limits
          reached