Add --version flag for printing the version

[kentquirk]

Which problem is this PR solving?

• Adds a --version command line switch to print the released version number and exit.

Short description of the changes

• Default the version string to "dev", which will be overridden during the build process
• Pre-parse the command line to see if the version flag was set
• If so, print and exit
• Remove the "required" flag from dataset and writekey so that it's possible to get a version without them
• Evaluate their existence after the version check