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, 25 insertions, 0 deletions

diff --git a/DynamicMeter.h b/DynamicMeter.h
new file mode 100644
index 00000000..3d1bc9f2
--- /dev/null
+++ b/DynamicMeter.h
@@ -0,0 +1,25 @@
+#ifndef HEADER_DynamicMeter
+#define HEADER_DynamicMeter
+
+#include "Meter.h"
+
+
+typedef struct DynamicMeter_ {
+   char name[32];  /* unique name, cannot contain spaces */
+   char* caption;
+   char* description;
+   unsigned int type;
+   double maximum;
+
+   void* dynamicData;  /* platform-specific meter data */
+} DynamicMeter;
+
+Hashtable* DynamicMeters_new(void);
+
+const char* DynamicMeter_lookup(const ProcessList* pl, unsigned int param);
+
+unsigned int DynamicMeter_search(const ProcessList* pl, const char* name);
+
+extern const MeterClass DynamicMeter_class;
+
+#endif