Add support for running wasm-snip

[fitzgen]

See also wasm-tool/rust-plugin#1 and #153

Basically there are four main options:

• Should we snip the std::panicking code? yes/no

• Should we snip the std::fmt code? yes/no

• Here are some specific functions to snip. (list of zero or more strings)

• Here are some regex patterns of functions to snip. (list of zero or more strings)

[ashleygwilliams]

following up on this feature request- do we still want to do this? how do we want to prioritize this?

[fitzgen]

do we still want to do this?

Yes, I believe so.

how do we want to prioritize this?

Not super high, in my opinion. I think the existing RFCs, wasm-opt support, and serve/watch are probably all higher priority.