Refactor the types.rs types and structures (#681)

* Refactor the `types.rs` types and structures

A few changes applied along the way:

* Documentation added to most methods and types.
* Limits are now stored with the maximum as optional rather than a
  sentinel u32 value for `None`.
* The `Name` type was removed in favor of just using a bare `String`.
* The `Extern` prefix in the varaints of `ExternType` has been removed
  since it was redundant.
* Accessors of `ExternType` variants no longer panic, and unwrapping
  versions were added with "unwrap" in the name.
* Fields and methods named `r#type` were renamed to `ty` to avoid
  requiring a raw identifier to use them.

* Remove `fail-fast: false`

This was left around since the development of GitHub Actions for
wasmtime, but they're no longer needed!

* Fix compilation of the test-programs code

* Fix compilation of wasmtime-py package

* Run rustfmt

crates/api/src/instance.rs

@@ -4,7 +4,7 @@ use crate::module::Module;
 use crate::r#ref::HostRef;
 use crate::runtime::Store;
 use crate::trampoline::take_api_trap;
-use crate::types::{ExportType, ExternType, Name};
+use crate::types::{ExportType, ExternType};
 use anyhow::Result;
 use std::cell::RefCell;
 use std::collections::{HashMap, HashSet};
@@ -122,7 +122,7 @@ impl Instance {
             .exports()
             .iter()
             .enumerate()
-            .find(|(_, e)| e.name().as_str() == name)?;
+            .find(|(_, e)| e.name() == name)?;
         Some(&self.exports()[i])
     }
 
@@ -141,7 +141,7 @@ impl Instance {
                 let _ = store.borrow_mut().register_wasmtime_signature(signature);
             }
             let extern_type = ExternType::from_wasmtime_export(&export);
-            exports_types.push(ExportType::new(Name::new(name), extern_type));
+            exports_types.push(ExportType::new(name, extern_type));
             exports.push(Extern::from_wasmtime_export(
                 store,
                 instance_handle.clone(),