Add newsfragments, remove defunct snapshot

newsfragments/468.bugfix.md

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+Calling `self.__init__()` now results in a nice error instead of a panic in the yul compilation stage.

newsfragments/468.feature.md

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+The analyzer now uses a query-based system, which fixes some shortcomings of the previous implementation.
+
+- Types can now refer to other types defined later in the file.
+Example:
+```
+type Posts = Map<PostId, PostBody>
+type PostId = u256
+type PostBody = String<140>
+```
+
+- Duplicate definition errors now show the location of the original definition.
+- The analysis of each function, type definition, etc happens independently, so an error in one
+doesn't stop the analysis pass. This means fe can report more user errors in a single run of the compiler.