This is akin to channels in Go, except:
* implemented in userland
* they are lock-free and thread-safe
* they integrate with the userland event loop
The self hosted compiler is changed to use a channel for events,
and made to stay alive, watching files and performing builds when
things change, however the main.zig file exits after 1 build.
Note that nothing is actually built yet, it just parses the input
and then declares that the build succeeded.
Next items to do:
* add windows and macos support for std.event.Loop
* improve the event loop stop() operation
* make the event loop multiplex coroutines onto kernel threads
* watch source file for updates, and provide AST diffs
(at least list the top level declaration changes)
* top level declaration analysis
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