Feature: Bulk Memory Operations

[bushidocodes]

This proposal may offer some performance improvements. I think the way we codegen passive data segments as initializer functions should map to the behavior below, but would require deeper study.

Instructions:

• memory.copy
• table.copy
• memory.fill
• memory.init
• table.init
• data.drop
• elem.drop

Reference: https://github.com/WebAssembly/bulk-memory-operations/blob/master/proposals/bulk-memory-operations/Overview.md