Add option --json-output (-j)

If given -j, format the output of -l and of searches as JSON.

tests/t_json

@@ -0,0 +1,25 @@
+#!/bin/sh
+
+set -e
+
+SDCV="$1"
+TEST_DIR="$2"
+
+unset SDCV_PAGER
+unset STARDICT_DATA_DIR
+
+test_json() {
+    PARAMS="$1"
+    EXPECTED=$(echo "$2" | jq 'sort')
+    RESULT=$($SDCV $PARAMS | jq 'sort')
+    if [ "$EXPECTED" != "$RESULT"]; then
+        echo "expected $EXPECTED but got $RESULT"
+        exit 1
+    fi
+}
+
+test_json "-x -j -l -n --data-dir \"$TEST_DIR\"" "[{\"name\": \"Test synonyms\", \"wordcount\": \"1\"},{\"name\": \"Sample 1 test dictionary\", \"wordcount\": \"1\"},{\"name\": \"test_dict\", \"wordcount\": \"1\"}]"
+test_json "-x -j -n --data-dir \"$TEST_DIR\" foo" "[{\"dict\": \"Test synonyms\",\"word\":\"test\",\"definition\":\"\nresult of test\"}]"
+test_json "-x -j -n --data-dir \"$TEST_DIR\" foobarbaaz" "[]"
+
+exit 0