Generic/FunctionCallArgumentSpacing: improve XML documentation

- `<documentation>` title now matches the sniff name
- Mention in the description that the sniff is about function and method
calls.
- `<standard>` and `<code>` descriptions now mention that the sniff also
checks for spaces before the comma.

Author: rodrigoprimo

src/Standards/Generic/Docs/Functions/FunctionCallArgumentSpacingStandard.xml

@@ -1,18 +1,18 @@
-<documentation title="Function Argument Spacing">
+<documentation title="Function Call Argument Spacing">
     <standard>
     <![CDATA[
-    Function arguments should have one space after a comma.
+    There should be no space before and exactly one space, or a new line, after a comma when passing arguments to a function or method.
     ]]>
     </standard>
     <code_comparison>
-        <code title="Valid: Single spaces after a comma.">
+        <code title="Valid: No space before and exactly one space after a comma.">
         <![CDATA[
 foo($bar,<em> </em>$baz);
         ]]>
         </code>
-        <code title="Invalid: No spaces after a comma.">
+        <code title="Invalid: A space before and no space after a comma.">
         <![CDATA[
-foo($bar,<em></em>$baz);
+foo($bar<em> </em>,<em></em>$baz);
         ]]>
         </code>
     </code_comparison>