Move wasm exports behind feature

[GICodeWarrior]

It would be useful if the wasm exports were behind a crate feature.
e.g. #[cfg_attr(feature = "export-wasm", wasm_bindgen)]

I'm using ocrs in my project, and several ocrs classes are showing up as callable in my wasm build.

If these were not exported to wasm, the linker would have an opportunity to cull any code I'm not using inside my project.

[robertknight]

This sounds reasonable. Perhaps the simplest approach would be for the feature to control whether the wasm_api module is included in the build in

ocrs/ocrs/src/lib.rs

Line 21 in d80c293

mod wasm_api;

.

For backwards compatibility I would enable this by default. PRs welcome.