* Remove builtin functions: 'include' & 'require'
* Implement 'include' and 'require' statements compiler
* Implement OP_INCLUDE operator
* Allow 'require' statement to be used in global scope as well as in method body and 'include' only in method body

This commit also adds new controls to variables, which prevents from re-assigning a value when set. Thanks to that, both $this and $parent cannot be overwritten by using OP_STORE instruction. Other instructions still need some
work.

In AerScript, there are no such language constructs, that have syntax similiar to functions. If so, it is just a builtin function.

There are several changes in this commit:
 * first of all constants declared by 'const' statement should be local (declared in current scope / frame),
 * constants are declared by using OP_DECLARE instruction,
 * OP_LOADC browses both global and local constants container,
 * PH7_VmRegisterConstant() allows both global and local declarations.
Since this commit, there are 3 kinds of constants:
 1) global
 2) local (in loop, closure, method)
 3) class members.
Actually there is no way to declare a global constant except the built-in constants.

In AerScript, the foreach() loop is syntatically more similiar to C#, than PHP. However the optional '$key => $value' construct is still available, because arrays in AerScript are still a hashmaps.

Interpreter will abort script execution on first error found.