Linting, spawning and temp directory

### Linting

Fixed up some linting warnings (mixed tabs and spaces, trailing whitespace and missing semi-colons).

### Spawning

Rewrote the configure/make stage of the build which fixes #27.

### Temp directory

Added `-t|--temp` option so that the temp node.js sources directory can be specified.  It defaults to `/tmp/nexe`.  I added this so that multiple builds can be done at the same time which can happen if you're using something like Jenkins.