MYNEWT-639 Add help text and check for pkg name 1) Update help text for "newt pkg new" to have package name input. 2) Error check that a package name is 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 "newt pkg remove" Usage help text
MYNEWT-639 Add help text and check for pkg name
1) Update help text for "newt pkg new" to have package name input.
2) Error check that a package name is 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 "newt pkg remove" Usage help text

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