use try-with-resources to close streams.

[gehel]

Some streams were not closed properly in case of exceptions. This commit introduces a few try-with-resources to properly close them.

[gehel]

Thanks for the project, this seem like a tool I'm going to use. My 6 year old received a Lunii for his birthday! I might be back with more contributions once I actually use the project. This first PR is a bit of a drive by commit (sorry for that) on a minor issue that just jumped to my eyes when looking over the code.