Update issue templates (#928)

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,39 @@
+---
+name: Feature request
+about: Suggest an idea for this project
+title: "[Feature request]"
+labels: ''
+assignees: ''
+
+---
+
+I propose we ... (describe your suggestion here)
+
+The existing way of Fantomas deals with this problem is ...
+
+## Pros and Cons 
+
+The advantages of making this adjustment to Fantomas are ...
+
+The disadvantages of making this adjustment to Fantomas are ...
+
+## Examples
+
+Please provide multiple examples (before and after scenarios) and explain what rules did apply to achieve the outcome.
+
+## Extra information
+
+Estimated cost (XS, S, M, L, XL, XXL): 
+
+Related suggestions: (put links to related suggestions here)
+
+## Affidavit (please submit!)
+
+Please tick this by placing a cross in the box:
+* [ ] I have [searched both open and closed suggestions on this site](http://github.com/fsharp/fslang-suggestions/issues) and believe this is not a duplicate
+
+Please tick all that apply:
+* [ ] This is not a breaking change to Fantomas
+* [ ] I or my company would be willing to help implement and/or test this
+* [ ] This suggestion is part of the [Microsoft style guide](https://docs.microsoft.com/en-us/dotnet/fsharp/style-guide/formatting) (please add a link to section if so)
+* [ ] This suggestion is part of the [G-Research style guide](https://github.com/G-Research/fsharp-formatting-conventions) (please add a link to section if so)