Added constants to interfaces

Added constants to interfaces. For the moment, constants can only be
used by using the full qualified name. For instance:

let myvar = MyProject\MyInterface:: MY_CONST;

Added forced regeneration of intermediate representation if
zephir-parser is updated (based on mtime).
Added better check to reconfigure the extension if files are
added/deleted.
Improvements of instanceof operator

The instanceof operator can now be used with variable right operands,
such as array_access and property_access in order to be able to write,
for instance:

if myObj instanceof this->classes[index] {
…
}
Enhanced instanceof compatibitily with PHP classes

Enhanced instanceof compatibitily with PHP classes and better support
of:
instanceof "<string>"
instanceof <variable>
instanceof <call>
instanceof <array_access>
instanceof <property_access>
Merge pull request #29 from mobli/master

Added constants to interfaces