cpustats lib - declare 'cpu_stats_read()' as in the header file

Signed-off-by: Davide Madrisan <davide.madrisan@gmail.com>
check_memory / meminfo lib - rework the used/cached/free memory stats

meminfo library: the memory usage calculation has been reviewed and is
now more accurate. The changes are based on the (long) discussions and
patches that have been recently posted in the procps mailing list.

check_memory: the command line options '-C|--caches' and '-a|--available'
now do nothing but are accepted for compatibility.

Signed-off-by: Davide Madrisan <davide.madrisan@gmail.com>
check_memory - make the option '-a|--available' available again

The option '-a|--available' will display the memory availabe (kernel 3.14+)
or the memory free (older kernels), instead of the memory used.

Signed-off-by: Davide Madrisan <davide.madrisan@gmail.com>
meminfo lib - 'MemAvailable' fall-back code for kernels 2.6.27+

A fallaback code has been added in order to provide the counter
'available memory' for the linux kernels 2.6.27 and above,

Signed-off-by: Davide Madrisan <davide.madrisan@gmail.com>
check_cpu: add one decimal digit to the counters cpu_*

Add one decimal digit to the counters 'cpu_user', 'cpu_system',
'cpu_idle', 'cpu_iowait', and 'cpu_steal' displayed in the
output message.

Signed-off-by: Davide Madrisan <davide.madrisan@gmail.com>