Use names to identify tensors (#61)

Closes #48.

ml.md

@@ -172,7 +172,7 @@ range from simple to complex (e.g., URLs?) and caching mechanisms of various kin
 <h5>Params</h5>
 <ul>
 <li><a name="set_input.ctx"><code>ctx</code></a>: <a href="#graph_execution_context"><a href="#graph_execution_context"><code>graph-execution-context</code></a></a></li>
-<li><a name="set_input.index"><code>index</code></a>: <code>u32</code></li>
+<li><a name="set_input.name"><code>name</code></a>: <code>string</code></li>
 <li><a name="set_input.tensor"><a href="#tensor"><code>tensor</code></a></a>: <a href="#tensor"><a href="#tensor"><code>tensor</code></a></a></li>
 </ul>
 <h5>Return values</h5>
@@ -196,7 +196,7 @@ expectation could be removed as a part of https://github.com/WebAssembly/wasi-nn
 <h5>Params</h5>
 <ul>
 <li><a name="get_output.ctx"><code>ctx</code></a>: <a href="#graph_execution_context"><a href="#graph_execution_context"><code>graph-execution-context</code></a></a></li>
-<li><a name="get_output.index"><code>index</code></a>: <code>u32</code></li>
+<li><a name="get_output.name"><code>name</code></a>: <code>string</code></li>
 </ul>
 <h5>Return values</h5>
 <ul>

wit/wasi-nn.wit

@@ -118,7 +118,7 @@ interface inference {
     init-execution-context: func(graph: graph) -> result<graph-execution-context, error>;
 
     /// Define the inputs to use for inference.
-    set-input: func(ctx: graph-execution-context, index: u32, tensor: tensor) -> result<_, error>;
+    set-input: func(ctx: graph-execution-context, name: string, tensor: tensor) -> result<_, error>;
 
     /// Compute the inference on the given inputs.
     ///
@@ -127,7 +127,7 @@ interface inference {
     compute: func(ctx: graph-execution-context) -> result<_, error>;
 
     /// Extract the outputs after inference.
-    get-output: func(ctx: graph-execution-context, index: u32) -> result<tensor-data, error>;
+    get-output: func(ctx: graph-execution-context, name: string) -> result<tensor-data, error>;
 }
 
 /// TODO: create function-specific errors (https://github.com/WebAssembly/wasi-nn/issues/42)