release version 2.1.1

increase version in node package

bump version 1.8.1

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