Introduce starts_with() and starts_with_ci()

Create user-defined functions to check whether a string contains a
certain prefix instead of messing around with strncmp() and
strncasecmp().

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/utils.c

@@ -1602,3 +1602,15 @@ asprintf(char **str, const char *format, ...)
 
 	return n;
 }
+
+int starts_with(const char *s, const char *p)
+{
+	for (; *p && *p == *s; s++, p++);
+	return (*p == '\0');
+}
+
+int starts_with_ci(const char *s, const char *p)
+{
+	for (; *p && tolower(*p) == tolower(*s); s++, p++);
+	return (*p == '\0');
+}