Log Message:
Update to 0.20

Upstream changes:
0.20 Thu May 12 21:11:00 GMT+2 2016
      - Fix //b by interpreting it as existing XPath expression
        RT #114345, reported by Alexander Hartmaier

0.19 Tue May 10 19:23:00 GMT+2 2016
      - Fix another bug in ':not(...)' by moving to an ad-hoc recursive
        descent parser, RT #114261
      - Allow single and double quotes for some attributes