Issue espeak-ng/espeak-ng#120

Allow to decrease the score in the rule by adding

docs/dictionary.md

 | Symbol      | Description |
 |-------------|-------------|
 | `@`         | A vowel follows somewhere in the word. |
-| `+`         | Force an increase in the score in this rule (may be repeated for more effect). |
+| `+`         | Force an increase in the score in this rule by 20 points (may be repeated for more effect). |
+| `<`         | Force an decrease in the score in this rule by 20 points (may be repeated for more effect). |
 | `S<number>` | This number of matching characters are a standard suffix, remove them and retranslate the word. |
 | `P<number>` | This number of matching characters are a standard prefix, remove them and retranslate the word. |
 | `Lnn`       | `nn` is a 2-digit decimal number in the range 01 to 20 Matches with any of the letter sequences which have been defined for letter group `nn` |

src/libespeak-ng/compiledict.c

 				case '+':
 					c = RULE_INC_SCORE;
 					break;
+				case '<': // Can't use - as opposite for + because it is used literally as part of word
+					c = RULE_DEC_SCORE;
+					break;
 				case '@':
 					c = RULE_SYLLABLE;
 					break;
 			state = 3;
 			p = buf;
 			if (input[ix+1] == ' ') {
-				fprintf(f_log, "%5d: Syntax error. Space after (\n", linenum);
+				fprintf(f_log, "%5d: Syntax error. Space after (, or negative score for previous rule\n", linenum);
 				error_count++;
 			}
 			break;

src/libespeak-ng/dictionary.c

 				case RULE_INC_SCORE:
 					add_points = 20; // force an increase in points
 					break;
+				case RULE_DEC_SCORE:
+					add_points = -20; // force an decrease in points
+					break;            // TODO schould check why '<' is shown as '!' in rules trace
 				case RULE_DEL_FWD:
 					// find the next 'e' in the word and replace by 'E'
 					for (p = *word + group_length; p < post_ptr; p++) {

src/libespeak-ng/translate.h

 #define RULE_NOVOWELS     29 // X no vowels up to word boundary
 #define RULE_SPELLING     31 // W while spelling letter-by-letter
 #define RULE_LAST_RULE    31
+#define RULE_DEC_SCORE    33 // <
 
 #define DOLLAR_UNPR     0x01
 #define DOLLAR_NOPREFIX 0x02