v8js 1.3.0

This release merges changes from V8Js for PHP 5.x (version 0.6.3) to PHP 7.0 branch.

New Features
- Allow to adjust the considered "amount of external memory" by objects exported to V8

Bug Fixes
- Pass back V8Object instances, don't re-wrap
- Retain object identity on 'return $this'
- Retain object identity on JS-side 'return this'
- Send LowMemoryNotification signals to V8 before imposing memory limit
- Fix build against V8 version 5.2 (deprecated WeakCallbackInfo & GetHiddenValue et al)
- Improve/Clarify README

Code Cleanup
- Removed support for "old-age" V8 versions (i.e. V8 < 4.6.76)
- Removed old examples and pre-phpt test script