Add Github issue and PR templates, plus contributing guidelines

* Closes #1450

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,29 @@
+<!---
+
+### Bug Reports
+
+Reporting a bug? If relevant, we recommend including:
+
+* Your OS name and version
+* The versions of tools you're using (e.g. `stack`, `yesod` `ghc`).
+* The versions of dependencies you're using
+
+For your convenience, we recommend pasting this script into bash and uploading the output [as a gist](https://gist.github.com/).
+
+```
+command -v sw_vers && sw_vers # OS X only
+command -v uname && uname -a # Kernel version
+command -v stack && stack --version
+command -v stack && stack ghc -- --version
+command -v stack && stack list-dependencies
+command -v yesod && yesod version
+```
+
+* Also, is there anything custom or unusual about your setup? i.e. new or prerelease versions of GHC, stack, etc.
+
+* Finally, if possible, please reproduce the error in a small script, or if necessary create a new Github repo with the smallest possible reproducing case. [Stack's scripting support](https://docs.haskellstack.org/en/stable/GUIDE/#script-interpreter) might be useful for creating your reproduction example.
+
+### Support
+
+Please direct support questions to [Stack Overflow](https://stackoverflow.com/questions/tagged/yesod) or the [Yesod Google Group](https://groups.google.com/forum/#!forum/yesodweb). If you don't get a response there, or you suspect there may be a bug in Yesod causing your problem, you're welcome to ask here.
+-->

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,14 @@
+Before submitting your PR, check that you've:
+
+- [ ] Bumped the version number
+- [ ] Documented new APIs with [Haddock markup](https://www.haskell.org/haddock/doc/html/index.html)
+- [ ] Added [`@since` declarations](http://haskell-haddock.readthedocs.io/en/latest/markup.html#since) to the Haddock
+
+After submitting your PR:
+
+- [ ] Update the Changelog.md file with a link to your PR
+- [ ] Check that CI passes (or if it fails, for reasons unrelated to your change, like CI timeouts)
+
+<!---Thanks so much for contributing! :)
+
+_If these checkboxes don't apply to your PR, you can delete them_-->

CONTRIBUTING.md

@@ -0,0 +1,58 @@
+# Contributing
+
+Thanks for your interest in contributing to Yesod! This file has some tips for developing Yesod and getting a pull request accepted.
+
+## Development
+
+Yesod is a mega-repo that contains many Haskell packages, each in a different directory. All the subprojects can be developed with Stack, using `stack <command> <subproject>`, e.g.
+
+* `stack build yesod-form`
+* `stack test yesod-auth`
+* `stack haddock yesod-websockets`
+
+If you'd like to test your changes in a full-fledged Yesod app, you can use Stack to build against it, e.g.:
+
+```
+packages:
+- '/path/to/this/repo/yesod-auth'
+```
+
+## Testing
+
+Tests are appreciated, but not required, for changes to Yesod.
+
+## Documentation
+
+All public APIs must be documented. Documenting private functions is optional, but may be nice depending on their complexity. Example documentation:
+
+```
+-- | Looks up the hidden input named "_token" and adds its value to the params.
+--
+-- ==== __Examples__
+--
+-- > request $ do
+-- >   addToken_ "#formID"
+--
+-- @since 1.5.4
+addToken_ :: Query -- ^ CSS selector that resolves to the @<form>@ containing the token.
+		  -> RequestBuilder site ()
+```
+
+Examples are appreciated, but not required, in documentation. Marking new APIs with `@since <version number>` is required.
+
+## Versioning
+
+Yesod packages roughly follow the Haskell Package Versioning Policy, MAJOR.MAJOR.MINOR.PATCH
+
+* MAJOR - Used for massive changes in the library
+* MAJOR - Used for smaller breaking changes, like removing functions or changed behavior of a function.
+* MINOR - Used for new public APIs
+* PATCH - Used for bug fixes and documentationc changes.
+
+If you feel there is ambiguity to a change (e.g. fixing a bug in a function, when people may be relying on the old broken behavior), you can ask in an issue or pull request.
+
+Unlike in the Package Versioning Policy, deprecations are not counted as MAJOR changes.
+
+## Changelog
+
+After you submit a PR, update the subproject's Changelog.md file with a link to your PR