Accept option to change the output folder name

[JerryHue]

yassgy by default has the distribution folder to be named dist. While the user may rename the folder to their liking, it is a nice addition for yassgy to create a folder with a specified name.

We may accept the name when calling the program through the command line, by accepting an option labelled --output or -o. If there is no output folder name provided, dist will be used as default.

Thus, if we wrote

./yassgy -i input.txt -o out

then a directory called out should be created.

In the absence of a value when the option appears, an error has to be shown:

./yassgy -i input.txt -o

This means that the output option is required.

[JerryHue]

Commit fd6255c addresses this.

However, right now this does not complete the requirements: an error message does not appear. Instead, the help message is shown.