ENH: Implementation Copy-paste tag in conv_template.py

Ability to paste same copied code segment at more than one place. It take care of main concerned of code duplication in template.

Implementation of copy and paste tag in <code>cove_template.py</code>
copy and paste tag
-----------------------
<b>Example</b>
Here is demo template
<pre>
/**begin copy 
 *@hi@
 */
<b>Hello! This is just a dummy line</b>
 /**end copy**/

First I will write some useless line, then include code pasted to variable 
hi as /**paste @hi@**/
</pre>

Output:
<pre>
First I will write some useless line, then include code pasted to variable 
hi as <b>Hello! This is just an dummy line</b>
</pre>

Example
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See modified <code>scalarmathmodule.c.src</code> with this pr.