add `v8pp::version()` function to return the library version string

Updated version to 1.7.0 in `package.json`, glob `*.cpp` files into the NPM package.
Print both V8 and v8pp versions in the test runner if `--version` command-line
option was supplied.

bump node package version 1.6.0

Added Node.js `engine >= 8.0.0` restriction to use V8 version 6.X

bump node package version 1.5.2

bump node package version 1.5.1

Allow to use `std::shared_ptr` with wrapped class arguments

Fixed a bug to use a reference or shared_ptr to wrapped class as a function argument.
Now have to supply `use_shared_ptr` boolean template argument to `call_from_v8` for
proper `class_<T, use_shared_ptr>` usage on function argument unwrapping.

Added a `convert<T, ref_from_shared_ptr>` specialization to use a reference
as a function argument for wrapped with `std::shared_ptr<T>` classes.

Added test cases.

Bump NPM package version to 1.4.1

Bump NPM package version to 1.4.0

Bump NPM package version to 1.3.1

Bump NPM package version to 1.3.0

Bump NPM package version to 1.2.1