This closes #40
This closes #40

1) Update help text for `newt pkg new` to have package name input.
2) Error check that a package name provided for the command.
3) Changed `libs/mylib` to `sys/mylib` in `newt pkg` help text to reflect latest source structure.
   (this change is not related to MYNEWT-639)
4) Added <package-name> argument to
ewt pkg remove\ Usage help text

apache/incubator-mynewt-newt,apache/incubator-mynewt-newt