Expose wasm_exceptions engine option to Ruby

[takahashim]

Closes #598.

Adds a dispatch arm in hash_to_config so the existing wasmtime::Config::wasm_exceptions method becomes reachable from Engine.new.

Verification

The reproducer from #598, before:

without options      : Wasmtime::Error: Could not build module: failed to parse WebAssembly module
wasm_exceptions: true: ArgumentError: Unknown option: :wasm_exceptions

After:

without options      : Wasmtime::Error: Could not build module: failed to parse WebAssembly module
wasm_exceptions: true: OK

[jbourassa]

Thanks!