All commands except series and composite.

Can initialise the trend in the one sided HP filter with the trend
estimated with the standard HP filter.

 - New class member tags

 - Member tags is a structure, initialized to empty.

 - Each user-defined field of this structure must be a vobs(o)*1 cell
   array (each element is associated to a variable).

 - To add a new tag name:

      >> o.tag('type')

 - To associate a tag value to a variable:

      >> o.tag('type', 'Consumption', 'Flow')

   the first argument is the tag name, the second argument is the name
   of the variable, the last argument is the value of the tag.

New ops class member.

Use mat instead of csv (tex and new ops members are not saved ion csv files).

This member keeps track of the transformations and operations on the
variables. The name of the variables is now constant.

isunix returns true for linux AND osx => First test if the patlaform
is osx (with ismac).

Added 's' flag to rmdir command.

Otherwise, some strings may be interpreted as regular expression. The
correct syntax for selecting variables with regular expression is:

o{'[\w*_US]'}

while

o{'\w*_US'}

is not correct. The user must explicitely state that s/he wants to
select variables with regular expression by beginning and closing the
string with square brackets.

When a wildcard parameter is detected, the string is converted to a
regular expression by adding opening and closing square brackets and
replacing the wildcard parameter by \w*.

Consequently, in the last example, if * is the wildcard parameter,
string '\w*_US' would be converted into '[\w\w*_US]'. That is the
reason why this commit changes the wildcard parameter to ~ (which is
not used in matlab's regular expressions).