docs: use correct terminology for 1024 bytes

Yes, I like kilobytes better than kibibytes (when I say kilobytes,
I generally mean 1024).  But since the term is ambiguous, it can't
hurt to say what we mean, by using both the correct name and
calling out the numeric equivalent.

* src/libvirt.c (virDomainGetMaxMemory, virDomainSetMaxMemory)
(virDomainSetMemory, virDomainSetMemoryFlags)
(virNodeGetFreeMemory): Tweak wording.
* docs/formatdomain.html.in: Likewise.
* docs/formatstorage.html.in: Likewise.

docs/formatstorage.html.in

@@ -234,11 +234,15 @@
         to sparsely allocate a volume. It does not have to honour requests
         for sparse allocation though.<br/>
         <br/>
-        By default this is specified in bytes, but an optional
+        By default this is specified in bytes, but an optional attribute
         <code>unit</code> can be specified to adjust the passed value.
-        Values can be: 'K' (kilobytes), 'M' (megabytes), 'G' (gigabytes),
-        'T' (terabytes), 'P' (petabytes), or 'E' (exabytes).
-        <span class="since">Since 0.4.1</span></dd>
+        Values can be: 'K' (kibibytes, 2<sup>10</sup> or 1024 bytes),
+        'M' (mebibytes, 2<sup>20</sup> or 1,048,576 bytes), 'G'
+        (gibibytes, 2<sup>30</sup> or 1,073,741,824 bytes), 'T'
+        (tebibytes, 2<sup>40</sup> or 1,099,511,627,776 bytes), 'P'
+        (pebibytes, 2<sup>50</sup> or 1,125,899,906,842,624 bytes), or
+        'E' (exbibytes, 2<sup>60</sup> or 1,152,921,504,606,846,976
+        bytes).  <span class="since">Since 0.4.1</span></dd>
       <dt><code>capacity</code></dt>
       <dd>Providing the logical capacity for the volume. This value is
         in bytes by default, but a <code>unit</code> attribute can be