Fix matlabserver shutdown behavior

[blink1073]

Fixes #168, addresses #164.

I could not find a way to reliably interrupt the Matlab process and recover from it, but at least now Ctrl+C results in a clean shutdown of the Matlab process.

[arokem]

Whoops. Sorry that it's taken so long to look at this. Looks good!

[isbadawi]

@blink1073 Can you explain why onCleanup is needed here?

I ask because it looks like Octave doesn't like you calling exit or quit inside an onCleanup handler, so this error always gets printed when we exit:

error: quit: not supported in embedded mode
error: called from:
error:    at line -1, column -1
error:   /Users/isbadawi/code/py/python-matlab-bridge/pymatbridge/matlab/matlabserver.m at line 12, column 1

[blink1073]

@isbadawi, it was needed to make sure Matlab actually shut down.

[blink1073]

You could try wrapping it in a try block.