[Scilab] remove targetversion argument

This commit handles multi-version support at runtime, it
fixes:
 * 5.5.2 - with cutted long identifier name
 * 6.0.0 - with full string identifier
 * 6.1.0 - with 1 or 0 output argument

It also improves the codebase by:
 * Using `Char(X)` instead of `DohCheck(X)` and `Data(X)`
 * Using `Len(X)` instead of `strlen()`
 * Correctly detecting old Scilab versions

Author: davidcl

Doc/Manual/Scilab.html

@@ -304,11 +304,6 @@ <H3><a name="Scilab_running_swig_options">36.2.5 Scilab command line options</a>
 <td>Generate the gateway XML with the given &lt;gateway_id&gt;</td>
 </tr>
 
-<tr>
-<td><tt>-targetversion</tt></td>
-<td>Generate for Scilab target (major) version</td>
-</tr>
-
 </table>
 
 <p>
@@ -343,10 +338,6 @@ <H3><a name="Scilab_wrapping_identifiers">36.3.2 Identifiers</a></H3>
 In these cases, the <a href="SWIG.html#SWIG_rename_ignore">%rename directive</a> can be used to choose a different Scilab name.
 </p>
 
-<p>
-Note: truncations can be disabled by specifying the target version 6 of Scilab in the <tt>targetversion</tt> argument (i.e. <tt>-targetversion 6</tt>).
-</p>
-
 <H3><a name="Scilab_wrapping_functions">36.3.3 Functions</a></H3>