Explore possible parser performance improvements so that Kin can do better "on the fly" syntax checking

[danielmartin]

As PR #29 shows, there's an opportunity for Kin to work not only in batch mode, but integrated with text editors and IDEs, doing checks in the background.

For a better experience, we should make the parser faster. Without leaving the convenience of using ANTLR, maybe we could massage the input grammar a little bit or memoize things so that the latency between checks is reduced and doesn't scale poorly as the Xcode project gets bigger.

[Serchinastico]

Absolutely right, we first did Kin just as a one-shot tool so we didn't think that much about performance back then, but there are plenty of possible improvements on that side, that's for sure.

We have to find some time to see how to do that specifically, though. In the meantime, any PR addressing the issue is more than welcome.