customTriggerProc option

When IAS is applied to the table, this option allows to move the trigger
out of it
Corrected behavior if triggerPageThreshold == 0

If triggerPageThreshold == 0, there is no point in binding to the
"scroll" event, and, if the next page data exists, trigger should be
shown immediately (not after scrolling as before).
Merge remote-tracking branch 'upstream/master'
readme update
Merge pull request #60 from yvanin/master

customTriggerProc and corrected behavior if triggerPageThreshold == 0