Constant area plugin done

Samo Penic

2019-03-08 5e08f27fac51e8f7261cd4484ab8878befac8fe1

 src/general.h

@@ -347,6 +347,7 @@
   ts_plugin_chain *vm_energy_after_execute;
   ts_plugin_chain *vm_before_montecarlo_constraint;
   ts_plugin_chain *vm_new_state_accepted;
   ts_plugin_chain *vm_new_state_rejected;
   ts_plugin_chain *cleanup;
} ts_plugin_chains;