Log Message:

(1) Bump the version 2.18 to 2.20
(2) The available patch to 2.20.1 has reject on gas/doc/as.info so on hold to \ 
the version
(3) The real Changes from 2.18 to 2.20 are too huge be listed here.
    And ChangeLog are split into many files, also with ChangeLog-200{7,8}
    etc. Please consult such files, thank you