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