Improve some of the scripts (won't get to all now).

• lint: simplify output to make problems easier to see
• lint: don't require user input to continue linting
• lint: don't stop linting after a linter failure
• lint & test: call version to generate Sources/MasKit/Package.swift
• bootstrap, build, format, lint, test & version: allow calling from any directory, not just from the project root
• bootstrap, build, format, lint, test & version: fail when accessing unset variable
• format & lint: improve swiftlint settings
• get swift-format from Homebrew instead of making it a dependency
• misc cleanup