WASM build fails (mac)

I tried to follow the instructions to [build for web](https://bfnightly.bracketproductions.com/rustbook/webbuild.html), but they fail on my 2019 macbook pro.

I've attached the errors I got, and I can confirm the wasm build works when I remove rltk from my dependencies in `Cargo.toml`

I also noticed a couple of things in the WASM tutorial that seem to be targeted towards windows users (like using `\` instead of `/` for paths) so I was wondering if the wasm stuff was only tested on windows.

Thanks for making this tutorial btw!

```
error[E0432]: unresolved import `platform::Signal`
--> /Users/ldd/.cargo/registry/src/github.com-1ecc6299db9ec823/ctrlc-3.1.9/src/lib.rs:52:9
|
52 | pub use platform::Signal;
| ^^^^^^^^^^^^^^^^ no `Signal` in `platform`

error[E0412]: cannot find type `Error` in module `platform`
--> /Users/ldd/.cargo/registry/src/github.com-1ecc6299db9ec823/ctrlc-3.1.9/src/error.rs:25:21
|
25 | impl From for Error {
| ^^^^^ not found in `platform`
|
help: consider importing one of these items
|
1 | use core::fmt::Error;
|
1 | use crate::Error;
|
1 | use crate::error::fmt::Error;
|
1 | use std::error::Error;
|
and 2 other candidates

error[E0412]: cannot find type `Error` in module `platform`
--> /Users/ldd/.cargo/registry/src/github.com-1ecc6299db9ec823/ctrlc-3.1.9/src/error.rs:26:26
|
26 | fn from(e: platform::Error) -> Error {
| ^^^^^ not found in `platform`
|
help: consider importing one of these items
|
1 | use core::fmt::Error;
|
1 | use crate::Error;
|
1 | use crate::error::fmt::Error;
|
1 | use std::error::Error;
|
and 2 other candidates

error[E0412]: cannot find type `Signal` in module `platform`
--> /Users/ldd/.cargo/registry/src/github.com-1ecc6299db9ec823/ctrlc-3.1.9/src/signal.rs:22:21
|
22 | Other(platform::Signal),
| ^^^^^^ not found in `platform`

error[E0425]: cannot find function `init_os_handler` in module `platform`
--> /Users/ldd/.cargo/registry/src/github.com-1ecc6299db9ec823/ctrlc-3.1.9/src/lib.rs:97:25
|
97 | match platform::init_os_handler() {
| ^^^^^^^^^^^^^^^ not found in `platform`

error[E0425]: cannot find function `block_ctrl_c` in module `platform`
--> /Users/ldd/.cargo/registry/src/github.com-1ecc6299db9ec823/ctrlc-3.1.9/src/lib.rs:110:27
|
110 | platform::block_ctrl_c().expect("Critical system error while waiting for Ctrl-C");
| ^^^^^^^^^^^^ not found in `platform`

error: aborting due to 6 previous errors

Some errors have detailed explanations: E0412, E0425, E0432.
For more information about an error, try `rustc --explain E0412`.
error: could not compile `ctrlc`
```