Support for gomobile as compiler target

[dlsniper]

At some point there should be support for using gomobile:

Build a shared library:

gomobile bind [-target android|ios] [-o output] [build flags] [package]

Compile APK or iOS app:

gomobile build [-target android|ios] [-o output] [build flags] [package]

Compile and install on Android:

gomobile install [-target android] [build flags] [package]

At the moment however I'm not able to compile things from command line so I can't provide better docs for this.

[monopole]

Also launching the freshly installed app, e.g. here's the full sequence with the 'basic' app:

  go get -d golang.org/x/mobile/example/basic
  $GOPATH/bin/gomobile build golang.org/x/mobile/example/basic
  $GOPATH/bin/gomobile install golang.org/x/mobile/example/basic
  # Then run it with:
  adb shell am start -n org.golang.todo.basic/org.golang.app.GoNativeActivity
  # or this hack with monkey:
  adb shell monkey -p org.golang.todo.basic 1 -