Add sum calculation functionality to dev CLI setup subcommand

[r6915ee]

The dev CLI's setup subcommand has a new feature that allows it to calculate the sha256 hash of the current libraries file, storing it into an ignored .sum file. Without the new --ignore-sum flag, if the hash of the current file and the hash presented in the sum file are the same, then the setup process won't continue. The primary use case of this that I see is to avoid having to reinstall the libraries in the case of #952, where the script would always be run every time the development shell was entered.

From the commit message:

The subcommand uses this feature to compare the sha256 sums of the previous and current
building/libs.xml files in order to decide whether or not to initiate the setup
process. It adds an --ignore-sum flag to immediately pass the check used for this.

This also clears up the help message for the subcommand in question, updates both
setup- scripts to allow for variable arguments, and adds --all as an alias for
--reinstall.

[Raltyro]

.sum?

[r6915ee]

.sum?

Those files simply contain the last sha256 hash that was created from the libs.xml file and are purely local. The subcommand reads the last hash from this file and compares it to the respective hash of the current libs.xml file to check whether or not libs.xml was modified.