Merge pull request/issue templates

.github/ISSUE_TEMPLATE/improvement.md

@@ -0,0 +1,28 @@
+---
+name: "Improvement"
+about: "A feature request or code improvement."
+---
+
+<!-- Please try to describe precisely what you would like to do in
+Cranelift/Wasmtime and/or expect from it. You can answer the questions below if
+they're relevant and delete this text before submitting. Thanks for opening an
+issue! -->
+
+#### Feature
+
+<!-- What is the feature or code improvement you would like to do in
+Cranelift/Wasmtime? -->
+
+#### Benefit
+
+<!-- What is the value of adding this in Cranelift/Wasmtime? -->
+
+#### Implementation
+
+<!-- Do you have an implementation plan, and/or ideas for data structures or
+algorithms to use? -->
+
+#### Alternatives
+
+<!-- Have you considered alternative implementations? If so, how are they
+better or worse than your proposal? -->