Use doxygen commands instead of HTML escapes

In our documentation, we show which header file to include for each
libcork module.  This patch updates those include lines to use the
doxygen \< and \> commands, instead of the HTML &lt; and &gt; escapes.
It just looks a bit cleaner.

include/libcork/core.h

@@ -19,7 +19,7 @@
 /**
  * @defgroup core Core module
  *
- * <tt>#%include &lt;libcork/core.h&gt;</tt>
+ * <tt>#%include \<libcork/core.h\></tt>
  */
 
 /*** order of groups in documentation ***/

include/libcork/core/byte-order.h

@@ -22,7 +22,7 @@
 /**
  * @addtogroup byte_order Byte order
  *
- * <tt>#%include &lt;libcork/core/byte-order.h&gt;</tt>
+ * <tt>#%include \<libcork/core/byte-order.h\></tt>
  *
  * This section contains definitions for determining the endianness of
  * the host system, and for byte-swapping integer values of various
@@ -37,7 +37,7 @@
  * @defgroup endianness Endianness detection
  * @ingroup byte_order
  *
- * <tt>#%include &lt;libcork/core/byte-order.h&gt;</tt>
+ * <tt>#%include \<libcork/core/byte-order.h\></tt>
  *
  * The macros in this section can be used to determine the endianness of
  * the current system.  We also provide a C string constant for the
@@ -160,7 +160,7 @@
  * @defgroup byteswap Byte swapping macros
  * @ingroup byte_order
  *
- * <tt>#%include &lt;libcork/core/byte-order.h&gt;</tt>
+ * <tt>#%include \<libcork/core/byte-order.h\></tt>
  *
  * The macros in this section can be used to swap integer values of
  * various sizes.  There are a couple variations for each integer types: