Import wasm memory and table?

[kripken]

In 0xc the wasm memory can be imported. This is useful for

• General emscripten integration, e.g. the filesystem initialization code can write to memory, so letting wasm import an existing memory avoids us needing the current mergeMemory hack we do (see src/js/wasm.js-post.js).
• Dynamic linking will also want to import memory, so always importing memory makes things simpler and more consistent.

Practically speaking, this should just need a few changes in src/js/wasm.js-post.js and then for asm2wasm and s2wasm to emit modules that import instead of export memory.

[kripken]

Similar logic motivates importing the table as well.

[kripken]

Memory and table importing implemented in 6c12d22 and f5a0be6 on the stack branch.

[kripken]

This was done.