RFC0027 - Snaps of Preview builds of PowerShell Core (#134)

@PowerShell/powershell-committee has approved this RFC with quorum from @HemantMahawar, @daxian-dbw, @BrucePay, @JamesWTruher, and @joeyaiello. Absent are @khansen00 and @SteveL-MSFT 

* initial draft of snap preview RFC
* fix typo
* address PR feedback
* fix spelling issue
* update comments due date
* add motivation for calling the preview build stable.
* Update and rename 4-Experimental-Accepted/RFCXXXX-Snap-Preview.md to 5-Final/RFC0027-Snap-Preview.md
* Add Committee decision for Snap package RFC

Author: TravisEz13

5-Final/RFC0027-Snap-Preview.md

@@ -0,0 +1,83 @@
+---
+RFC: RFC
+Author: Travis Plunk (@TravisEz13)
+Status: Final
+Version: 0.1
+Area: Packaging
+Comments Due: July 15, 2018
+Plan to implement: Yes
+---
+
+# Snaps of Preview builds
+
+We currently have not published any [Snap packages](https://snapcraft.io) of a preview build.  There are some significant questions before we do.
+Primarily, do we follow Snap's model of channels or do we have a separate package called `powershell-preview`.
+I propose we have a separate package as it will allow side-by-side installation with the stable Snap and will be consistent with our Linux package names.
+
+## Motivation
+
+Snaps are easy to use and having a Snap of the preview would allow people to adopt the preview across a wide variety of platforms.
+We want to design the preview Snap in a way that allows for the preview Snap to be installed easily without losing access to the stable version of PowerShell.
+
+## Specification
+
+* There shall be two Snap packages available:
+  * Stable: a production-ready, supported build, called `powershell`.
+  * Preview: an unsupported build that may contain incomplete new features and high-impact bugs,
+    and should therefore not be used in production, called `powershell-preview`.   Our hope is that the development process ensures that every build is stable and high quality.
+* Aliases
+  * Stable package: `pwsh`
+  * Preview package: `pwsh-preview`
+* Snap channels
+  * Stable package: Will always use the `stable` channel, because it is stable.
+  * Preview package: Will always use the `stable` channel, because the package name and version indicates the quality.
+    * Alternative: Preview builds could use the `edge` channel, and release candidates could use the `candidate` channel.
+      This would mean you would always have to use the one of the following commands to install `sudo snap install powershell-preview --edge --classic` or `sudo snap install powershell-preview --candidate --classic`
+
+## Alternate Considerations and Proposals
+
+### Use Snap's model of channels
+
+The main dis-advantage here is that preview builds cannot be install side-by-side with a stable build (at least with Snap alone).  Snap does allow you to switch between things you have downloaded fairly quickly so this is not fatal.
+
+* There shall be one Snap package available:
+  * Called `powershell`.
+* Alias
+  * `pwsh`
+* Snap channels
+  * Stable builds would be published to the stable channel and installed using the following command:
+    `sudo snap install powershell --classic`
+  * Release Candidate builds would be published to the stable channel and installed using the following command:
+    `sudo snap install powershell --classic --candidate`
+  * Preview builds would be published to the stable channel and installed using the following command:
+    `sudo snap install powershell --classic --edge`
+
+## Open Questions
+
+---------------
+## PowerShell Committee Decision
+
+### Voting Results
+
+Joey Aiello: Accept
+
+Bruce Payette: Accept
+
+Steve Lee: Absent
+
+Hemant Mahawar: Accept
+
+Jim Truher: Accept
+
+Dongbo Wang: Accept
+
+Kenneth Hansen: Absent
+
+### Majority Decision
+
+We support side-by-side and want to keep it that way, hence the distinct packages.
+The alias names also make sense given the pattern we set with the existing Linux packages.
+
+### Minority Decision
+
+N/A