- alias sim
- No real logic is added

- use cobra to bind command line flag
- use logrus for logging

which introduced a lot of packages

- Add machine simulator config struct, which supports: num, start, end, step
- add util function for read config file in test (TODO: don't know if it will have sideffect if is called multiple times)

- the machine.go is already 150+ lines with current dumbest simulation logic,
so should put it in sub package and split to several files
- Add format script in Ayi, which will call gofmt

- machine is the pojo and factory for machine
- simulator is the real machine simulator

- intial time and value sub package under generator
- add fixed interval
- add constant
- TestNewGenerator shows it is working

- add functions ending with New, in order to have old code as example, will remove old and change name after migration
- add value generator interface
- when generate default machine, add seriesWithValueGenerater into machine
- machine has different array for keep int and double series

- see TestMachineSimulatorNew
- TODO: why I saw more cpu_core=3 in log ouput
- TODO: remove old generator code

- generate machine
- add default machine
- start
- related property and methods in simulator interface

- delete interface for point generator
- delete constant int point generator
- delete series with point generator

- the simulator config struct is actually never used
- TODO: not output in current default setting, might be problem with config file

It seems the serializer is not properly initialized
````
DEBU[0000] enable debug logging                          pkg=x.util
DEBU[0000] config file xephon-b.yml is loaded            pkg=x.cmd
DEBU[0000] triggered simulator command                   pkg=x.cmd
DEBU[0000] machine simulator start                       pkg=x.s.machine
DEBU[0000] need to serialize                             pkg=x.s.machine
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x28 pc=0x498eed]

goroutine 21 [running]:
panic(0x7bc3e0, 0xc420016120)
	/home/at15/app/go/src/runtime/panic.go:500 +0x1a1
github.com/xephonhq/xephon-b/pkg/simulator/machine.(*MachineSimulator).Start.func2(0xc42007cde0, 0xc4200aa630, 0xc42007ce40, 0xc42017c290)
	/home/at15/workspace/src/github.com/xephonhq/xephon-b/pkg/simulator/machine/simulator.go:84 +0x11d
created by github.com/xephonhq/xephon-b/pkg/simulator/machine.(*MachineSimulator).Start
	/home/at15/workspace/src/github.com/xephonhq/xephon-b/pkg/simulator/machine/simulator.go:92 +0x20e
````

- treated output as encoding and cased the null pointer problem
- change example num to 3 for less output when try the command
- run `xb sim --debug --type json` to see json output
- TODO: json serialize should have `\n` in order to be read by others

- ignore *.dat file as its the default output file suffix

- TODO: use append may not be the most efficient way. But adding a wrapper for writer might be more messy
since the writer should know little(nothing) about the serializer

- though it seems file without calling f.Close