Keep opt-level = s and remove console_error_panic_hook

[kylebarron]

Saves 331KB on the uncompressed default wasm bundle.

Although this actually makes the brotli-compressed wasm bundle 1kb larger!! Though the gzip-compressed wasm bundle is still 60kb smaller.

Brotli encoded wasm sizes (with arrow1):

• opt-level = s with console_error_panic_hook: 855246
• opt-level = s without console_error_panic_hook: 824049
• opt-level = z with console_error_panic_hook: 856203
• opt-level = z without console_error_panic_hook: 855934

So let's go with opt-level = s and without console_error_panic_hook as the default

Closes #45