Replace tabs with spaces in html docs

wkhtmltopdf is not expanding tabs within <pre> elements to 8 spaces as it
should. Workaround the problem by converting all tabs to an appropriate
number of spaces.

Doc/Manual/Arguments.html

@@ -60,7 +60,7 @@ Suppose you had a C function like this:
 
 <div class="code"><pre>
 void add(double a, double b, double *result) {
-	*result = a + b;
+  *result = a + b;
 }
 </pre></div>
 
@@ -204,7 +204,7 @@ input value:
 </p>
 
 <div class="code"><pre>
-int *INPUT		
+int *INPUT
 short *INPUT
 long *INPUT
 unsigned int *INPUT
@@ -221,7 +221,7 @@ function:
 
 <div class="code"><pre>
 double add(double *a, double *b) {
-	return *a+*b;
+  return *a+*b;
 }
 </pre></div>
 
@@ -273,7 +273,7 @@ These methods can be used as shown in an earlier example. For example, if you ha
 
 <div class="code"><pre>
 void add(double a, double b, double *c) {
-	*c = a+b;
+  *c = a+b;
 }
 </pre></div>
 
@@ -339,7 +339,7 @@ A C function that uses this might be something like this:</p>
 
 <div class="code"><pre>
 void negate(double *x) {
-	*x = -(*x);
+  *x = -(*x);
 }
 
 </pre></div>