Fixes options overriding

In `wrapper` the global options could be overridden but this could cause problems with subsequent calls to `exec`.  For example

    exec.quiet('ls'); // Quiet, as expected.
    exec.interactive('vim');  // Now also quiet due to the call above.

The global options seemed a bit odd to me and felt a bit inconsistent in their usage so I removed them completely.  This might impact on whether you accept the pull request.

Also I've cleaned up some linting warnings.