0.8.0

• (breaking change) JS errors are now mapped to their proper Crystal exceptions. i.e. JS SyntaxError becomes Duktape::SyntaxError.
• (breaking change) Make all exception classes more consistent. Instances of Duktape::Error are all recoverable exceptions that are thrown by the engine at runtime (eg. Duktape::TypeError). Instances of Duktape::InternalError are generally non-recoverable for a given context (eg. Duktape::HeapError).
• Added call_success, call_failure and return_undefined convenience methods that provide the appropriate integer status codes when returning from a native function call.
• Added the push_global_proc method that simplifies pushing a named native function to the stack.
• Duktape::Runtime instances may now accept a execution timeout value in milliseconds upon creation. [#15, @raydf].
• Changed the name in the shard.yml from duktape.cr to duktape. This should have no effect on the installation process.