Added CHANGELOG.md entry on syntax-only generic methods.

CHANGELOG.md

Index: CHANGELOG.md
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index 32c31724e794a6aff9eb94fb46051efb34562c10..93739409b54aa646e87766eab983cadf57cf889e 100644
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+++ b/CHANGELOG.md
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 ### Language
 
+* Support generic methods with erasure. This feature does not introduce
+  full-fledged support for generic methods, but it bridges the gap to a
+  full implementation. It allows for declaring type parameters on methods,
+  passing actual type arguments in function and method invocations, and
+  getting static checks from the analyzer. The missing part is reification
+  of type arguments at runtime. For details please check the
+  [informal specification](https://gist.github.com/eernstg/4353d7b4f669745bed3a5423e04a453c).

[Lasse Reichstein Nielsen, 2016/11/28 08:55:45]

I think this is somewhat too wordy for a CHANGES entry. Can we make it short and
crisp? Don't say what it doesn't do, don't say what it might do later, just say
what we have right now.

Maybe something like:

* Allow *writing* generic functions and function calls. The type arguments are
removed at runtime, but the analyzer is allowed to use them for warnings. This
allows writing strong-mode compatible code that can also be used by spec-mode
programs. 
See [informal
specification](https://gist.github.com/eernstg/4353d7b4f669745bed3a5423e04a453c)
for more information.

 * Don't warn about switch case fallthrough if the case ends in a `rethrow`
   statement.
 * Also don't warn if the entire switch case is wrapped in braces - as long as