WASM / no_std updates for the verifying utilities

[drewstone]

@gakonst this is a wip. We'd like to get the verifier related utilities working in Substrate, currently it throws no_std related errors when including such logic in a Substrate runtime. Is there any insight you can provide here on how we may update this repo to make this possible?

Running with cargo build --release --no-default-features --target wasm32-unknown-unknown still throws with

error: the wasm32-unknown-unknown target is not supported by default, you may need to enable the "js" feature. For more information see: https://docs.rs/getrandom/#webassembly-support
   --> /Users/drew/.cargo/registry/src/github.com-1ecc6299db9ec823/getrandom-0.2.7/src/lib.rs:235:9
    |
235 | /         compile_error!("the wasm32-unknown-unknown target is not supported by \
236 | |                         default, you may need to enable the \"js\" feature. \
237 | |                         For more information see: \
238 | |                         https://docs.rs/getrandom/#webassembly-support");
    | |________________________________________________________________________^

error[E0433]: failed to resolve: use of undeclared crate or module `imp`
   --> /Users/drew/.cargo/registry/src/github.com-1ecc6299db9ec823/getrandom-0.2.7/src/lib.rs:262:5
    |
262 |     imp::getrandom_inner(dest)
    |     ^^^ use of undeclared crate or module `imp`