No longer use a month-by-month directory structure when HISTORY is
greater than 28

This patch updates sa1 and sa2 shell scripts in order to no longer use
the tree of directories that used to be created in the /var/log/sa
directory when HISTORY was greater than 28.
Now, when HISTORY is greater than 28, sadc is called with option -D to
create data files named saYYYYMMDD. All these files are located in the
same directory.
This patch also updates the sysstat parameters file to add a new
variable: SA_DIR, which gives the directory where sa and sar files are
saved.

Signed-off-by: Sebastien GODARD <sysstat@users.noreply.github.com>
Add new ZIP variable to sysstat parameters file

Add the new ZIP variable to sysstat parameters file.
This variable contains the program used to compress data and reports
files.

Signed-off-by: Sebastien GODARD <sysstat@users.noreply.github.com>
Update documentation

Update the FAQ and various manual pages to document recent changes (new
variables added to sysstat parameters file, new naming convention for
standard system activity daily data and report files, etc.)

Signed-off-by: Sebastien GODARD <sysstat@users.noreply.github.com>