Break up feature test macro names so the table doesn't fall off the page

Author: jaredhoberock

general.html

@@ -47,7 +47,7 @@ <h1>Feature-testing recommendations</h1>
           <td>P0155R0</td>
           <td>Task Block R5</td>
           <td><cxx-ref to="parallel.task_block"></cxx-ref></td>
-          <td><code>__cpp_lib_experimental_parallel_task_block</code></td>
+          <td><code>__cpp_lib_experimental_-</code><br><code>parallel_task_block</code></td>
           <td>201711</td>
           <td>
             <code>&lt;experimental/exception_list&gt;</code><br>
@@ -58,7 +58,7 @@ <h1>Feature-testing recommendations</h1>
           <td>P0076R4</td>
           <td>Vector and Wavefront Policies</td>
           <td><cxx-ref to="parallel.execpol.unseq"</cxx-ref>, <cxx-ref to="parallel.execpol.vec"</cxx-ref></td>
-          <td><code>__cpp_lib_experimental_execution_vector_policy</code></td>
+          <td><code>__cpp_lib_experimental_-</code><br><code>execution_vector_policy</code></td>
           <td>201711</td>
           <td>
             <code>&lt;experimental/algorithm&gt;</code><br>
@@ -69,15 +69,15 @@ <h1>Feature-testing recommendations</h1>
           <td>P0075R2</td>
           <td>Template Library for Parallel For Loops</td>
           <td><cxx-ref to="parallel.alg.reductions"</cxx-ref>, <cxx-ref to="parallel.alg.inductions"</cxx-ref>, <cxx-ref to="parallel.alg.forloop"</cxx-ref></td>
-          <td><code>__cpp_lib_experimental_parallel_for_loop</code></td>
+          <td><code>__cpp_lib_experimental_-</code><br><code>parallel_for_loop</code></td>
           <td>201711</td>
           <td><code>&lt;experimental/algorithm&gt;</code></td>
         </tr>
         <tr>
           <td><ins>P0214R9</ins></td>
           <td><ins>Data-Parallel Vector Types & Operations</ins></td>
           <td><ins><cxx-ref to="parallel.simd"</cxx-ref></ins></td>
-          <td><ins><code>__cpp_lib_experimental_parallel_simd</code></ins>
+          <td><ins><code>__cpp_lib_experimental_-</code><code>parallel_simd</code></ins>
           <td><ins>201803</ins></td>
           <td><ins><code>&lt;experimental/simd&gt;</code></ins></td>
         </tr>