Add script compilation and caching

This release adds script compilation and caching. Also more new methods added and some internal logic refactored. See detailed changes below.

As of this release, V8 >= 5.8.168 required.

* - BC-breaking or potentially BC-breaking changes

Changes to public API and other important changes which may affect end-user:

• * Add $is_wasm and $is_module options to V8\ScriptOriginOptions and V8\ScriptOrigin;
• * Remove non-standard V8\Scrip::{getSource,getOrigin};
• * Remove V8\ObjectValue::{Get,Set,Has,Delete,CreateDataProperty}Indexed methods;
• * Remove non-working V8\Context extensions support;
• * Handle V8\IntegerValue sub-types when returning values from V8, fixes #19;
• Add V8\UnboundScript class;
• Add V8\ScriptCompiler\CachedData class;
• Add V8\ScriptCompiler\CompileOptions class;
• Add V8\ScriptCompiler\Source class;
• Add V8\ScriptCompiler;
• Add V8\SymbolValue::GetToPrimitive() method;
• Add V8\Value::IsNullOrUndefinedl() method;
• Add more V8\Value::Is*() methods;
• Add V8\MapObject;
• Add V8\SetObject;
• Fix obj and func templates external memory adjusting.

Improvements and new methods

In this PR new methods added and some internal logic refactored.

As of this release, V8 >= 5.4.420 required.

Also, deprecated or soon to be deprecated API calls are removed in this release, see note on BC-breaking changes below.

• add V8\Isolate::IsInUse() method.
• add V8\AdjustableExternalMemoryInterface interface;
• add V8\ObjectValue::AdjustExternalAllocatedMemory() method;
• add V8\ObjectValue::GetExternalAllocatedMemory() method;
• add V8\FunctionTemplate::AdjustExternalAllocatedMemory() method;
• add V8\FunctionTemplate::GetExternalAllocatedMemory() method;
• add V8\ObjectTemplate::AdjustExternalAllocatedMemory() method;
• add V8\ObjectTemplate::GetExternalAllocatedMemory() method;
• rewrite callbacks structures to use std containers;
• use realistic external allocated memory value to notify isolate about based on callbacks structures size and optionally specified by user value.
• add V8\Value::TypeOf() method;
• add V8\ObjectValue::IsConstructor() method;
• add V8\ObjectValue::SetIntegrityLevel() method;
• add V8\CallbackInfo::InContext() method;
• add V8\ReturnValue::InContext() method;
• add V8\ReturnValue::Get() method;
• add V8\HeapStatistics::malloced_memory() method;
• add V8\HeapStatistics::peak_malloced_memory() method;
• properly shutdown in case of OOM;
• simplify V8\ReturnValue internals and integration with callbacks.

BC breaking changes:

• V8\ObjectValue::ForceSet() removed in a favor of V8\ObjectValue::DefineOwnProperty(), V8\ObjectValue::CreateDataProperty() and V8\ObjectValue::CreateDataPropertyIndex().

First release

This is a first public release.

PHP 7 only (>= 7.0), including PHP 7.1.

This release works best with V8 Google JavaScript engine version 5.2 installed. At this time extension tested using 5.2.371.

For Ubuntu there are pinepain/libv8-5.2 PPA. To install fresh libv8 do:

$ sudo add-apt-repository ppa:pinepain/libv8-5.2 -y
$ sudo apt-get update -q
$ sudo apt-get install -y libv8-5.2-dev

For OS X there are v8.rb homebrew formula. To install fresh libv8 do:

$ brew install https://raw.githubusercontent.com/pinepain/php-v8/v0.1.0/scripts/homebrew/v8.rb

No windows support at this time, though, there should be nothing preventing to add it except of getting how to properly package V8 itself for windows.