Character substitution in file names can lead to collisions

[Lukas-Stuehrk]

When generating file names for symbols, swift-doc replaces some characters of the symbol's name with underscore (_).

This can lead to the problem that it produces the same file name for different symbols with different names. The second symbol then overwrites the page of the previously declared symbol.

This happens rather often with operators:

infix operator >>>
public func >>> (lhs: String, rhs: String) { }

infix operator <<<
public func <<< (lhs: String, rhs: String) { }

Both create the file ___.

But it can also happen for any other symbol:

public class Outer {
    public struct Inner {}
}

public class Outer_Inner {}

Both symbols create the file Outer_Inner.

[mattt]

Related to #258