Added support for executing a script from file or from stdin

[ksmith3036]

Sometimes several operations will be executed in close succession. To avoid the seemingly costly operation of initializing the programs connection to OneDrive, the possibility to execute several commands in one go seems nice to have. The pull request adds the following commands:

script <scriptfile>
reads and executes a script from file

script -
reads and executes commands from stdin. This may both be used for piping scripts into the program, or using it as a simple OneDrive shell.