Add support for interpolated string handlers annotated with the attribute

[Emik03]

The goal is to implement the following behavior:

• Inspect every string interpolation on the project.
• Get the type of the parameter. Continue only if it is an interpolated string handler as oppose to System.String.
• Connect $"foo" and $"{foo:foo}" onto AppendFormatted and AppendLiteral overloads, respectively.
  • Check if the parameter of AppendFormatted and AppendLiteral has a Match attribute, if it does, match it against the interpolation.
  • If it doesn't, check the parameter types of the function. If a parameter has an implicit conversion to either System.String (for value and format) or System.Int32 (for alignment).
    • Go to the type's implicit conversion function and get the parameters.
    • For each parameter, get the attributes for Match.
    • If they exist, test each Match against the literal value that was passed into the specific expression of the string interpolation.

This is a very complicated spec, and as such will likely take a very long time to implement.

Tests have already been added, which at the time of writing is currently failing: 45311dd

Once all tests pass, version 2.1 will be released, assuming no other breaking features are rolled out.