Enchant the debugging capabilities

[JBenda]

• add documentation for existing summary envs (J_TRACE and J_TRACE_FUNCTION)
• add KEEP_STACK as option for J_TRACE_FUNCTION to trace stacks below traced function

e.g.:
J_TRACE=summary J_TRACE_FUNCTION=j_message_send ./hello_world →

# stack duration[s] count
j_message_send 0.000237 8  

J_TRACE=summary J_TRACE_FUNCTION=j_message_send,KEEP_STACK ./hello_world →

# stack duration[s] count
j_batch_execute/j_batch_execute_internal/j_batch_execute_same/j_kv_put_exec/j_message_send 0.000026 1
j_batch_execute/j_batch_execute_internal/j_batch_execute_same/j_db_insert_exec/j_backend_db_func_exec/j_message_send 0.000029 1
j_batch_execute/j_batch_execute_internal/j_batch_execute_same/j_kv_put_exec/j_connection_pool_pop/j_connection_pool_pop_internal/j_message_send 0.000022 1
j_batch_execute/j_batch_execute_internal/j_batch_execute_same/j_object_write_exec/j_message_send 0.000031 1
j_batch_execute/j_batch_execute_internal/j_batch_execute_same/j_db_schema_create_exec/j_backend_db_func_exec/j_message_send 0.000027 1
j_batch_execute/j_batch_execute_internal/j_batch_execute_same/j_db_schema_create_exec/j_backend_db_func_exec/j_connection_pool_pop/j_connection_pool_pop_internal/j_message_send 0.000036 1
j_batch_execute/j_batch_execute_internal/j_batch_execute_same/j_object_create_exec/j_connection_pool_pop/j_connection_pool_pop_internal/j_message_send 0.000039 1
j_batch_execute/j_batch_execute_internal/j_batch_execute_same/j_object_create_exec/j_message_send 0.000030 1   

J_TRACE=summary J_TRACE_FUNCTION=j_message_send,j_object* ./hello_world →

# stack duration[s] count
j_object_create_exec/j_message_send 0.000044 2
j_message_send 0.000111 6
j_object_create_exec 0.013171 1