Enhancement - Sequence range limiting

- Prevents overly large ranges.  A bug was reported from a user
  who tried this:

    % task annotate 1 1-987654321

  The 1-987654321 was assumed to be a valid range, and caused task
  to consume all available memory.  The workaround was:

    % task 1 annotate 1-987654321

  But it seems a good idea to range-limit sequences.  Currently
  it is 1000.  Perhaps this should be configurable.

src/Sequence.h

@@ -30,6 +30,8 @@
 #include <vector>
 #include <string>
 
+#define SEQUENCE_MAX 1000
+
 class Sequence : public std::vector <int>
 {
 public: