Lack of easy way to append to text files.

[trilleplay]

After reading though lunduniversity/introprog#782 I think that some of the issues associated with Bank's saving and loading could be addressed by introducing a method that lets the user easily append to text files (since it might feel natural to do so in doEvent.)

I propose that a method be added for appending lines.

[bjornregnell]

Thanks for contributing! For completeness there should also be an appendString method that appends a string, similar to how saveLines also has a counterpart saveString.
Ideally this would use the underlying appendability in java.io, see e.g. https://stackoverflow.com/a/24982850
See also #47

[trilleplay]

Thanks for contributing! For completeness there should also be an appendString method that appends a string, similar to how saveLines also has a counterpart saveString. Ideally this would use the underlying appendability in java.io, see e.g. https://stackoverflow.com/a/24982850 See also #47

It's been a while, but I've made the requested changes to my PR, I think I've written something that is what you're looking for @bjornregnell .

[bjornregnell]

@trilleplay You may want to see the correct implementation here to handle both empty seq and trailing newline: 482dcce

[bjornregnell]

I have also added some tests: c80904a