Add batch mode

[phil294]

So that multiple statements can be issued and parsed and executed at once. Doing this could improve the performance of tkbash many times over.

This could be done with a new option - or maybe by reading standard input. The option parsing and execution section at the end would need to be wrapped accordingly.

Alternative idea (probably worse in terms of complexity to the tkbash user): Change --debug option so that the generated output can be reused without tkbash. For this to work, a big bunch needs to be rewritten, so better go with option A.