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/trampoline/table.rs

@@ -10,11 +10,7 @@ pub fn create_handle_with_table(table: &TableType) -> Result<InstanceHandle> {
 
     let table = wasm::Table {
         minimum: table.limits().min(),
-        maximum: if table.limits().max() == std::u32::MAX {
-            None
-        } else {
-            Some(table.limits().max())
-        },
+        maximum: table.limits().max(),
         ty: match table.element() {
             ValType::FuncRef => wasm::TableElementType::Func,
             _ => wasm::TableElementType::Val(table.element().get_wasmtime_type()),