Common generate script

[bmulvihill]

While creating a generator for acronym and noticed how each exercise had it own generate script. This leads to a lot of code duplication since each script is almost identical.

This PR would allow for a single generate script that takes an exercise name as the argument, and regenerates the exercise. If the exercise is not found and error message will display. I tested it out on all the exercises and I had to modify two generators to ensure consistent naming.

Example usage:
bin/generate raindrops

Let me know if this is something that would be helpful!

[kotp]

This looks good to me.

How does the contributors documentation need to be changed to communicate this change, if it does, or is it a drop in replacement?

[Insti]

Nice @bmulvihill, This is something I'd been planning on doing when I found some time, but it looks like you beat me to it.

[bmulvihill]

@kotp @Insti the contributing doc would need to change slightly. I can update it in this PR. I can also remove all the old generate scripts.

[kotp]

That would be awesome!

[bmulvihill]

@kotp @Insti Ok this should be good to go

[kotp]

Was blocking #454