Added more tests + fixed evstr issues

tests/ev_str/replace_first_query_too_long.c

@@ -0,0 +1,18 @@
+#define EV_STR_IMPLEMENTATION
+#include "ev_str.h"
+
+#include <assert.h>
+
+int main(void)
+{
+  evstring text = evstr("ab");
+  evstring replacement = evstr("x");
+  evstring query = evstr("abc");
+
+  evstring result = evstring_replaceFirst(text, query, replacement);
+
+  assert(EV_EQUAL(evstring)(&result, &text));
+
+  evstring_free(result);
+  return 0;
+}