djspiewak#15: Add githubPublishTo setting

README.md

@@ -134,5 +134,13 @@ The following setting keys are defined:
 - `githubRepository : String` The repository which hosts this project under the organization/user defined in the other setting
 - `githubTokenSource : TokenSource` (*defaults to `Environment("GITHUB_TOKEN")`*) Where the plugin should go to read the GitHub API token to use in authentication. `TokenSource` has two possible values: `Environment(variable: String)` and `GitConfig(key: String)`. You can compose multiple sources together using `||`, which will result in each being attempted in order from left to right. This is mostly just a convenience. You're free to do whatever you want. Just don't, like, put it in your build. 
 - `githubSuppressPublicationWarning : Boolean` (*defaults to `false`*) If you're just using this plugin as a means to *resolve* artifacts, not to publish them, the publication warning may serve as an annoyance more than anything else. Setting this to `true` will suppress the normal warning text when you fail to define `githubOwner` or `githubRepository`.
+- `githubPublishTo : Option[Resolver]` The default `publishTo` target for GitHub Packages. This setting is useful for switching `publishTo` target to [sbt-sonatype](https://github.com/xerial/sbt-sonatype) or GitHub Packages: 
+
+```scala
+// Switch publishTo target for using Sonatype if RELEASE_SONATYPE env is true, 
+// otherwise publish to GitHub Packages:
+val RELEASE_TO_SONATYPE = sys.env.getOrElse("RELEASE_SONATYPE", "false").toBoolean 
+publishTo := if(RELEASE_SONATYPE) sonatypePublishTo.value else githubPublishTo.value
+```
 
 `homepage` and `scmInfo` will be automatically set for you if `githubOwner` and `githubRepository` are themselves set.

src/main/scala/sbtghpackages/GitHubPackagesKeys.scala

@@ -25,6 +25,8 @@ trait GitHubPackagesKeys {
   val githubTokenSource = settingKey[TokenSource]("Where to get the API token used in publication (defaults to github.token in the git config)")
 
   val githubSuppressPublicationWarning = settingKey[Boolean]("Whether or not to suppress the publication warning (default: false, meaning the warning will be printed)")
+
+  val githubPublishTo = taskKey[Option[Resolver]]("publishTo setting for deploying artifacts to GitHub packages")
 }
 
 object GitHubPackagesKeys extends GitHubPackagesKeys

src/main/scala/sbtghpackages/GitHubPackagesPlugin.scala

@@ -55,7 +55,8 @@ object GitHubPackagesPlugin extends AutoPlugin {
     })
 
   val packagePublishSettings = Seq(
-    publishTo := {
+    publishTo := githubPublishTo.value,
+    githubPublishTo := {
       val suppress = githubSuppressPublicationWarning.value
       val log = streams.value.log
       val ms = publishMavenStyle.value