Upgrade to Crystal 0.24.1

[faultyserver]

Crystal 0.24.0 is currently a pre-release, though in actuality the content of the release has been static for a while.

I think it'd be a good idea to get ahead of the curve and upgrade the Crystal version before the next minor release of Myst. There are a few features that I'm really looking forward, but mainly better stacktraces, including locations on macOS and this bugfix for Constant manipulation inside a static method (14a79e0 has more details) :)

As for an upgrade path, I know there are a few TODOs in the codebase that reference Crystal 0.24, so those should be evaluated with this (though they won't necessarily be resolved by it). Also, expect_raises in the specs will now require an exception type to be given. In most cases, these should already be given as ParseError or SyntaxError, but may need to be added.

A successful resolution to this issue will be compiling with --release on Crystal 0.24.0.

[faultyserver]

0.24.1 has been tagged for release, so this upgrade should be coming sooner rather than later.

[faultyserver]

Crystal 0.24.1 has been properly released and binaries are available. Not sure how long it will take to propagate to brew and apt, but this should finally be a realistic goal :)

[faultyserver]

Brew finally updated and travis is running 0.24.1, so now I can finally start on this.