update doc
now will try to use php array notation everywhere, unless jstrue or jsobj. later I will fix  to proper scope...
remove variable name resolver val() , now 100% use php array. but, buggy when {{this}} , later fix it.
fix for {{this}}
fix for parent trace
fix for php ['name'] issue when  is a string
remove unused getVariableArray, fix block start/end validation.
refine many unit test for new interface
refine unit tests for new interface
fix wrong end tag warning
remove unused args. also fix custom helper
use level to compute parent stacks
add secdec to record context special case when running section
fix for block helpers
refine seclvl logic. some doc update
use count(), it only cost 1% more cpu time, but reduce compile complexity a lot.
no need maintain secdec logic now
Merge branch 'master' into php_array_parent
update doc.
fix for unit test