unload the extension, while closing the Matlab process.

Also: error handling when no Matlab process is running.
Get the matlab instance from the ip instance registry.
Fix indentation error, no need for the kwargs to the unload function.
Use 'pop' to also remove the magic from the registry, while you're at it.
Merge pull request #8 from jenshnielsen/master

Install matlab files in private dir
Merge pull request #6 from arokem/unload

unload the extension, while closing the Matlab process.