Add support for markdown rendering (#144)

* Write a markdown parser

* Hide the markdown rendering behind a feature flag

* Apply the markdown rendering on the paragraph element

* Support nested emphasis

* Seperate the lexing and the parsing

* Add a performance test

* Move the rendering upwards to the markdown class

* Clean up a bit

* Remove the statement from the paragraph again

As a precaution, until I figure out where to go from here.

* Throw an error due to missing activation

* Revert last commit

* Apply auto escaping to markdown string

Sources/HTMLKit/Framework/Rendering/Markdown/Extensions/Markdown+Character.swift

@@ -0,0 +1,114 @@
+import Foundation
+
+extension Character {
+
+    /// A boolean value indicating whether this character represents an asterisk (U+002A).
+    internal var isAsterisk: Bool {
+
+        if self == "\u{002A}" {
+            return true
+        }
+
+        return false
+    }
+
+    /// A boolean value indicating whether this character represents a comma (U+005F).
+    internal var isUnderscore: Bool {
+
+        if self == "\u{005F}" {
+            return true
+        }
+
+        return false
+    }
+
+    /// A boolean value indicating whether this character represents a tilde (U+007E).
+    internal var isTilde: Bool {
+
+        if self == "\u{007E}" {
+            return true
+        }
+
+        return false
+    }
+
+    /// A boolean value indicating whether this character represents a back tick (U+0060).
+    public var isBackTick: Bool {
+
+        if self == "\u{0060}" {
+            return true
+        }
+
+        return false
+    }
+
+    /// A boolean value indicating whether this character represents a left square bracket (U+005B).
+    public var isLeftSquareBracket: Bool {
+
+        if self == "\u{005B}" {
+            return true
+        }
+
+        return false
+    }
+
+    /// A boolean value indicating whether this character represents a right square bracket (U+005D).
+    public var isRightSquareBracket: Bool {
+
+        if self == "\u{005D}" {
+            return true
+        }
+
+        return false
+    }
+
+    /// A boolean value indicating whether this character represents a left parenthesis (U+0028).
+    public var isLeftParenthesis: Bool {
+
+        if self == "\u{0028}" {
+            return true
+        }
+
+        return false
+    }
+
+    /// A boolean value indicating whether this character represents a right parenthesis (U+0029).
+    public var isRightParenthesis: Bool {
+
+        if self == "\u{0029}" {
+            return true
+        }
+
+        return false
+    }
+
+    /// A boolean value indicating whether this character represents a solidus (U+002F).
+    public var isSolidus: Bool {
+
+        if self == "\u{002F}" {
+            return true
+        }
+
+        return false
+    }
+
+    /// A boolean value indicating whether this character represents a colon (U+003A).
+    public var isColon: Bool {
+
+        if self == "\u{003A}" {
+            return true
+        }
+
+        return false
+    }
+
+    /// A boolean value indicating whether this character represents a period (U+002E).
+    public var isPeriod: Bool {
+
+        if self == "\u{002E}" {
+            return true
+        }
+
+        return false
+    }
+}