Improved documentation and test cases for Expression Manager:
(1) index.php/admin/expressions/functions - now lists all available functions and links to function reference (e.g. PHP manual for cases where it follows exactly that syntax)
(2) syntax highlighting now shows the meaning and syntax of functions as tool tips
(3) refactored array defining functions to make it easier to build GUI for using these functions

git-svn-id: file:///Users/Shitiz/Downloads/lssvn/source/limesurvey_ci@10894 b72ed6b6-b9f8-46b5-92b4-906544132732