Add a new DynamicMeter class for runtime Meter extension

This commit is based on exploratory work by Sohaib Mohamed.
The end goal is two-fold - to support addition of Meters we
build via configuration files for both the PCP platform and
for scripts ( https://github.com/htop-dev/htop/issues/526 )

Here, we focus on generic code and the PCP support.  A new
class DynamicMeter is introduced - it uses the special case
'param' field handling that previously was used only by the
CPUMeter, such that every runtime-configured Meter is given
a unique identifier.  Unlike with the CPUMeter this is used
internally only.  When reading/writing to htoprc instead of
CPU(N) - where N is an integer param (CPU number) - we use
the string name for each meter.  For example, if we have a
configuration for a DynamicMeter for some Redis metrics, we
might read and write "Dynamic(redis)".  This identifier is
subsequently matched (back) up to the configuration file so
we're able to re-create arbitrary user configurations.

The PCP platform configuration file format is fairly simple.
We expand configs from several directories, including the
users homedir alongside htoprc (below htop/meters/) and also
/etc/pcp/htop/meters.  The format will be described via a
new pcp-htop(5) man page, but its basically ini-style and
each Meter has one or more metric expressions associated, as
well as specifications for labels, color and so on via a dot
separated notation for individual metrics within the Meter.

A few initial sample configuration files are provided below
./pcp/meters that give the general idea.  The PCP "derived"
metric specification - see pmRegisterDerived(3) - is used
as the syntax for specifying metrics in PCP DynamicMeters.

1 files changed, 2 insertions, 2 deletions

diff --git a/linux/LinuxProcessList.c b/linux/LinuxProcessList.c
index 7452c199..6f86d021 100644
--- a/linux/LinuxProcessList.c
+++ b/linux/LinuxProcessList.c
@@ -184,11 +184,11 @@ static void LinuxProcessList_updateCPUcount(ProcessList* super, FILE* stream) {
    }
 }
 
-ProcessList* ProcessList_new(UsersTable* usersTable, Hashtable* pidMatchList, uid_t userId) {
+ProcessList* ProcessList_new(UsersTable* usersTable, Hashtable* dynamicMeters, Hashtable* pidMatchList, uid_t userId) {
    LinuxProcessList* this = xCalloc(1, sizeof(LinuxProcessList));
    ProcessList* pl = &(this->super);
 
-   ProcessList_init(pl, Class(LinuxProcess), usersTable, pidMatchList, userId);
+   ProcessList_init(pl, Class(LinuxProcess), usersTable, dynamicMeters, pidMatchList, userId);
    LinuxProcessList_initTtyDrivers(this);
 
    // Initialize page size