Refine license rules selectivity

This commit improves a few existing license rules to be more selective
adding either required phrasesz or minimum coverage.

Signed-off-by: Philippe Ombredanne <pombredanne@nexb.com>

Author: pombredanne

src/licensedcode/data/rules/gpl-2.0-font.SPDX.RULE

@@ -5,7 +5,7 @@ minimum_coverage: 10
 notes: license text as published by SPDX
 ---
 
-insert GPL v2 text here
+{{insert GPL v2 text here}}
 
 Font Exception
-As a special exception, if you create a document which uses this font, and embed this font or unaltered portions of this font into the document, this font does not by itself cause the resulting document to be covered by the GNU General Public License. This exception does not however invalidate any other reasons why the document might be covered by the GNU General Public License. If you modify this font, you may extend this exception to your version of the font, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.
+As a special exception, if you create a document which uses this font, and embed this font or unaltered portions of this font into the document, this font does not by itself cause the resulting document to be covered by the GNU General Public License. This exception does not however invalidate any other reasons why the document might be covered by the GNU General Public License. If you modify this font, you may extend this exception to your version of the font, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.

src/licensedcode/data/rules/gpl-3.0_23.RULE

@@ -13,7 +13,7 @@ ignorable_urls:
     - http://www.gnu.org/philosophy/why-not-lgpl.html
 ---
 
-GNU General Public License v3.0 - GNU Project - Free Software Foundation (FSF)
+{{GNU General Public License v3.0}} - GNU Project - Free Software Foundation (FSF)
 http://www.gnu.org/licenses/gpl-3.0.rdf
 
 GNU GENERAL PUBLIC LICENSE
@@ -698,4 +698,4 @@ into proprietary programs.  If your program is a subroutine library, you
 may consider it more useful to permit linking proprietary applications with
 the library.  If this is what you want to do, use the GNU Lesser General
 Public License instead of this License.  But first, please read
-  "http://www.gnu.org/philosophy/why-not-lgpl.html" http://www.gnu.org/philosophy/why-not-lgpl.html .
+  "http://www.gnu.org/philosophy/why-not-lgpl.html" http://www.gnu.org/philosophy/why-not-lgpl.html .

src/licensedcode/data/rules/unknown-license-reference_240.RULE

@@ -1,7 +1,6 @@
 ---
 license_expression: unknown-license-reference
-is_license_notice: yes
-relevance: 100
+relevance: 70
+is_license_clue: yes
 ---
-
-Used with permission
+Used with permission