Added the possibility to return a subsample from a dynSeries.

If ts is a dynSeries object, then the following syntax is valid:

t0 = dynDate('1950Q1') ;
t1 = dynDate('2000Q3') ;

range = t0:t1 ;
ds = ts(range);

Note that the dates in range do not need to be contiguous or sorted in increasing order.
Removed useless addpath commands in unitary tests.
Added a new interface to instantiate dynDate objects.

Call dynDate constructor with two arguments: teh first one is a 2*1 vector of integers (for time), the second one is a scalar integer (for freq).
Added the possibility to extract a dynDate object from a dynDates object.

*Example* If a dynDates object is built as follows

d1 = dynDate('1966Q4');
d2 = dynDate('2013Q1');
dd = d1:d2;

then dd(2) is a dynDate object (should be equal to dynDate('1967Q1')).
Added data file for unitary tests (dynSeries class).
Fixed bug.
Added the possibility to create a sub dynDates object. Added unitary test.

*Example* Let dd be a dynDate object:

d1 = dynDate('1966Q4');
d2 = dynDate('2013Q1');
dd = d1:d2;

then dd(2:5) is also dynDates object for the dates 1967Q1, 1967Q2, 1967Q3 and 1967Q5.
Moved shiftS function.
Completed header.
Rewrote @dynDates/subsref method recursively. Improved error messages.
Fixed unitary tests. @dynDates/sort and @dynDates/unique methods have to be called without (empty) parenthesis.