Define acronyms and add URL related to hash functions (#141)

Related to PR php/doc-en#3630

Author: jimwins

entities/acronyms.xml

@@ -150,6 +150,18 @@
     <simpara>Hyperwave Information Server</simpara>
    </listitem>
   </varlistentry>
+  <varlistentry>
+   <term>HKDF</term>
+   <listitem>
+    <simpara>HMAC Key Definition Function</simpara>
+   </listitem>
+  </varlistentry>
+  <varlistentry>
+   <term>HMAC</term>
+   <listitem>
+    <simpara>Hash-based Message Authentication Code</simpara>
+   </listitem>
+  </varlistentry>
   <varlistentry>
    <term>HTML</term>
    <listitem>
@@ -246,6 +258,12 @@
     <simpara>Network News Transfer Protocol</simpara>
    </listitem>
   </varlistentry>
+  <varlistentry>
+   <term>PBKDF2</term>
+   <listitem>
+    <simpara>Password-Based Key Derivation Function 2</simpara>
+   </listitem>
+  </varlistentry>
   <varlistentry>
    <term>PDF</term>
    <listitem>

entities/global.ent

@@ -113,6 +113,7 @@
 <!ENTITY url.gnu.configure "http://www.airs.com/ian/configure/">
 <!ENTITY url.gnupg "http://www.gnupg.org/">
 <!ENTITY url.gpgme "http://www.gnupg.org/related_software/gpgme/">
+<!ENTITY url.hash.nist-hash-functions "https://csrc.nist.gov/projects/hash-functions">
 <!ENTITY url.hp.software "http://software.hp.com/">
 <!ENTITY url.hpux.installguide "http://www.tekwire.net/joomla/building/apache/http-hpux-11-11">
 <!ENTITY url.iana.locale.subtags "http://www.iana.org/assignments/language-subtag-registry">