-chart flag causes exception on Windows

[richclement]

Hi,

When running tastypl on Windows, if I include the -chart option, the run will fail. This is because when creating the chart, the rpl.png file is being placed in the /tmp folder. If that does not exist, which it does not by default on Windows, then the run fails.

The quick fix is to create a folder at C:\tmp.

Session:

C:\tastypl> .\tastypl-v0.1-1-win.exe -input .\market.csv -printpl -positions -stats -chart > output.txt
F0713 15:32:59.597036   33640 tastypl.go:1186] open /tmp/rpl.png: The system cannot find the path specified.
goroutine 1 [running]:
github.com/golang/glog.stacks(0xc042083300, 0xc0420b2000, 0x6d, 0xbd)
        /go/src/github.com/golang/glog/glog.go:769 +0xd6
github.com/golang/glog.(*loggingT).output(0x757360, 0xc000000003, 0xc04211a210, 0x6f010f, 0xa, 0x4a2, 0x0)
        /go/src/github.com/golang/glog/glog.go:720 +0x328
github.com/golang/glog.(*loggingT).printDepth(0x757360, 0x3, 0x1, 0xc042acc810, 0x1, 0x1)
        /go/src/github.com/golang/glog/glog.go:646 +0x130
github.com/golang/glog.(*loggingT).print(0x757360, 0x3, 0xc042acc810, 0x1, 0x1)
        /go/src/github.com/golang/glog/glog.go:637 +0x61
github.com/golang/glog.Fatal(0xc042acc810, 0x1, 0x1)
        /go/src/github.com/golang/glog/glog.go:1128 +0x5a
main.dumpChart(0xc0422b6030, 0xe63, 0x1000, 0x0)
        /go/src/github.com/gotasty/tastypl/tastypl.go:1186 +0x128f
main.main()
        /go/src/github.com/gotasty/tastypl/tastypl.go:1220 +0x3a0

I would personally be fine with either the app putting the image into the executing folder or if /tmp does not exist, making the folder.