Aer/TODO

TODO list for typehinting branch.
Below list contains things that should be changed/fixed/implemented.


1. The debug_backtrace() does not show information about arrays type.
 * This is caused by ph7_context_new_array() creating a generic array w/o data type set.
   Most probably more builtin functions returning an array are affected.

2. PH7 pass and return arrays by reference. This behaviour should be changed and a copy of array should be made instead.

3. All builtin functions should be reworked. Actually they can return any value, sometimes of different type than declared.
   This causes errors during script execution.