Proposed change: newtmgr commands into cmd package

[Gordon Chaffee]

Hi folks,

I've made a change in https://github.com/apache/incubator-mynewt-newt/pull/3
off the develop branch that reorganizes the newtmgr commands that were
defined in newtmgr.go into a cmd package, and it splits each top level
command into a separate file.

The structure in the newtmgr area with this proposed change would be:

incubator-mynewt-newt/newtmgr/
incubator-mynewt-newt/newtmgr/cli/
incubator-mynewt-newt/newtmgr/protocol/
incubator-mynewt-newt/newtmgr/transport/
incubator-mynewt-newt/newtmgr/cmd/
    config.go
    connprofile.go
    echoctrl.go
    echo.go
    image.go
    logs.go
    mpstats.go
    parse.go
    stats.go
    taskstats.go
    usage.go

Let me know if there any objections to this restructuring.

Thanks,
Gordon