This is not necessary since ordering in INFO should not matter, also
this option is not available in Octave 5.x.

The round function in octave does not admit two arguments (the second
being the rounding precision) as in recent versions of Matlab. The same
trick should apply to old Matlab versions, but I do not know when
Mathworks introduced the second argument… A simple solution could be
to always use this trick, and never use the second argument.

This reverts commit 933c51d5.

 - daily to monthly
 - daily or monthly to quaterly

Conversion to annual frequency is not yet implemented, but this is
enough to close #1.

Four time aggregation methods are available:

 - 'sum' (aggregation of flow variables),
 - 'end-of-period' (aggregation of stock variables),
 - 'arithmetic-average', (aggregation of rates), and
 - 'geometric-average' (aggregation of ratios)

Examples:

>> a = dseries(rand(2*365+1,1), '2000-01-01')

a is a dseries object:

           | Variable_1
2000-01-01 | 0.26032
2000-01-02 | 0.56927
2000-01-03 | 0.24877
2000-01-04 | 0.3193
2000-01-05 | 0.9108
2000-01-06 | 0.88522
2000-01-07 | 0.79459
2000-01-08 | 0.92581
2000-01-09 | 0.17884
2000-01-10 | 0.51754
           |
2001-12-21 | 0.035016
2001-12-22 | 0.03975
2001-12-23 | 0.98857
2001-12-24 | 0.68618
2001-12-25 | 0.37669
2001-12-26 | 0.50432
2001-12-27 | 0.7635
2001-12-28 | 0.048875
2001-12-29 | 0.72593
2001-12-30 | 0.70133
2001-12-31 | 0.45889

>> dseries2Q(a, 'sum')

ans is a dseries object:

       | Variable_1
2000Q1 | 46.6096
2000Q2 | 45.1456
2000Q3 | 45.0172
2000Q4 | 47.6164
2001Q1 | 49.9093
2001Q2 | 46.2334
2001Q3 | 47.4685
2001Q4 | 47.1611

>> dseries2M(a, 'sum')

ans is a dseries object:

        | Variable_1
2000M1  | 16.7499
2000M2  | 15.4311
2000M3  | 14.4286
2000M4  | 14.3583
2000M5  | 15.7072
2000M6  | 15.0801
2000M7  | 14.2406
2000M8  | 15.9174
2000M9  | 14.8592
2000M10 | 17.5525
2000M11 | 13.3236
2000M12 | 16.7404
2001M1  | 18.9293
2001M2  | 16.1282
2001M3  | 14.8518
2001M4  | 16.9843
2001M5  | 14.5768
2001M6  | 14.6723
2001M7  | 14.9768
2001M8  | 15.3968
2001M9  | 17.0949
2001M10 | 15.0376
2001M11 | 16.6848
2001M12 | 15.4388

>> dseries2Q(dseries2M(a, 'sum'), 'sum')

ans is a dseries object:

       | Variable_1
2000Q1 | 46.6096
2000Q2 | 45.1456
2000Q3 | 45.0172
2000Q4 | 47.6164
2001Q1 | 49.9093
2001Q2 | 46.2334
2001Q3 | 47.4685
2001Q4 | 47.1611

Conversion of daily dates objects to lower frequency.

Frequency is passed as a member of the dates class.

Also removed reference to weekly frequency.

Also added and updated unit tests.