Added Markdown link and backslash escape support

[htinlinn]

The parser stack has been restructured and a new step has been introduced to allow for matching different opening and closing symbols. As a result, it's likely slower but way more flexible. Backslash escape support (issue #2) was also added to be able to parse URLs that might include parentheses in them.

[phillfarrugia]

Nice! I specifically like that you've improved the use of types like Rule, Token, Symbol to be more declarative of the behavior of different operations 😀 👌🏻

[phillfarrugia]

is there a specific reason you used a while loop as opposed to for (index, element) in <collection>.enumerated()?

i.e. this would remove the need to increment i each time

for (index, token) in tokens.enumerated() {
    // Process each token here
}

[htinlinn]

I am using a while loop here because, in the case of parsing links, I am iterating through two tokens at once; the enumerated for loop wouldn't let me do the same.

[phillfarrugia]

minor, but in some places you define extensions as explicitly internal, whereas in others you leave the protection level ommitted.

[htinlinn]

Yeah. I'll update this throughout the app to be consistent.

[phillfarrugia]

something minor I came across very recently actually, is in a file like this you're not actually using Foundation for anything (like NSObject, so this import is useless) you could actually remove it if you wanted to. I don't think there's any benefit other than conciseness though

[htinlinn]

Yeah. I try remove it when I remember but, most of the time, I don't.

[Xodia]

Approving but some issue with links with less than 4 chars (eg: [HELLO](mail://))

[ghvg1313]

Simple logic, good job

[htinlinn]

@Xodia seems like the issue was only with a beta version of Xcode.