Update docs by mentioning Groovy function and advising not to use javascript or Beanshell anymore for performances.
Update docs by mentioning Groovy function and advising not to use javascript or Beanshell anymore for performances.

git-svn-id: 5ccfe34f605a6c2f9041ff2965ab60012c62539a@1763866 13f79535-47bb-0310-9956-ffa450edef68

vherilier/jmeter,ra0077/jmeter,ubikloadpack/jmeter,max3163/jmeter,ubikloadpack/jmeter,vherilier/jmeter,etnetera/jmeter,ra0077/jmeter,max3163/jmeter,ra0077/jmeter,etnetera/jmeter,vherilier/jmeter,max3163/jmeter,etnetera/jmeter,etnetera/jmeter,ubikloadpack/jmeter,ra0077/jmeter,etnetera/jmeter,max3163/jmeter,vherilier/jmeter,ubikloadpack/jmeter