* Update the project to Swift 5.4
- Splash now uses the Swift 5.4 toolchain.
- Since Swift 5.4 now enables automatic test discovery on all supported
platforms, all of the infrastructure that was previously used to maintain
Linux unit testing compatibility has now been removed.
* Remove LinuxMain.swift
While Splash has supported iOS since its early days, this change makes
it possible to compile the iOS version as a Swift Package, using Xcode 11.
The changes require us to not make the assumption that != macOS == Linux.
(Also git ignore the new `.swiftpm` directory that SwiftPM now uses)
This change adds a new command line tool to the Splash family:
`SplashMarkdown`.
It’s an adapted version of the tool that I’ve been using for months to
publish every article on Swift by Sundell, and works by replacing all
code blocks within a Markdown file.
Adding this will hopefully make Splash even easier to use, without the
need for writing custom tooling, or to manually replace each code block
within a Markdown file with a “splashed” version.
This patch makes `HTMLOutputFormat` correctly escape all < and > characters
that occur in source code. Otherwise, a web browser rendering the resulting
HTML will interpret those characters as tags.
