Replace YAML-unsafe characters with �

Things like control character would invalidate whole report.  If user
needs verbatim, jat__submit() shall do that.

src/jat.sh.skel

@@ -1321,11 +1321,12 @@ __jat__writelog() {
     #
     # Write logged output (copy if needed)
     #
-    case $JAT__YLOG in
-        "") cat >> "$__JAT__SDIR/log.yaml" ;;
-        -)  tee -a "$__JAT__SDIR/log.yaml" ;;
-        *)  tee -a "$__JAT__SDIR/log.yaml" >> "$JAT__YLOG" ;;
-    esac
+    __jat__strip4yaml \
+      | case $JAT__YLOG in
+            "") cat >> "$__JAT__SDIR/log.yaml" ;;
+            -)  tee -a "$__JAT__SDIR/log.yaml" ;;
+            *)  tee -a "$__JAT__SDIR/log.yaml" >> "$JAT__YLOG" ;;
+        esac
 }
 
 __jat__valid_beid() {
@@ -1344,6 +1345,31 @@ __jat__valid_pair() {
     grep -qx '\([tor][.]\)\?[[:alpha:]_][[:alnum:]_]*=.*' <<<"$tainted"
 }
 
+__jat__strip4yaml() {
+    #
+    # Replace yaml-invalid characters
+    #
+    # Yaml won't allow all characters:
+    #
+    # > [...] The allowed character range explicitly excludes the C0 control
+    # > block #x0-#x1F (except for TAB #x9, LF #xA, and CR #xD which are
+    # > allowed), DEL #x7F, the C1 control block #x80-#x9F (except for NEL
+    # > #x85 which is allowed), the surrogate block #xD800-#xDFFF, #xFFFE,
+    # > and #xFFFF.
+    #
+    # so take stdin and replace all unacceptable characters with '�'.
+    #
+    local bad           # perl 'tr///' range of bad characters
+    local repl='�'      # replacement char
+    bad+='\N{U+0}-\N{U+8}\N{U+B}\N{U+C}\N{U+E}-\N{U+1F}'    # C0 with some gaps
+    bad+='\N{U+7F}'                                         # DEL alone
+    bad+='\N{U+80}-\N{U+84}\N{U+86}-\N{U+9F}'               # C1 with NEL gap
+    #   bad+='\N{U+D800}-\N{U+DFFF}'                        # surrogates
+    #   bad+='\N{U+FFFE}-\N{U+FFFF}'                        # 0xFFFE and 0xFFFF
+    #FIXME: for some reasons perl complains about these ^^
+    perl -CS -Mutf8 -pe "tr/$bad/$repl/"
+}
+
 __jat__yamls() {
     #
     # Print a scalar field named $1 with value $2