[code] Search function in the code Toolbox.

When the user types a letter, the toolbox scrolls to the first row that begins
with said letter (without considering if it is lower or upper case). If
there is not such a row, the toolbox scrolls to the first row that has a
letter higher than the typed letter.

Change-Id: I353d23560d8a4d618d96426c393b024e7fb487af

liba/include/ctype.h

@@ -4,5 +4,6 @@
 int isupper(int c);
 int isxdigit(int c);
 int isdigit(int c);
+int tolower(int c);
 
 #endif

liba/src/ctype.c

@@ -11,3 +11,7 @@ int isxdigit(int c) {
 int isdigit(int c) {
   return (c >= '0' && c <= '9');
 }
+
+int tolower(int c) {
+  return isupper(c) ? 'a' + c - 'A' : c;
+}