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().