Prepare release 3.0.0-M1 (#1452)

Pull request: #1452

build.sbt

@@ -3,7 +3,7 @@ import scalatex.ScalatexReadme
 lazy val readme = ScalatexReadme(
   projectId = "readme",
   wd = file(""),
-  url = "https://github.com/com-lihaoyi/Ammonite/tree/master",
+  url = "https://github.com/com-lihaoyi/Ammonite/tree/main",
   source = "Index"
 ).settings(
   scalaVersion := "2.12.18",

readme/Footer.scalatex

@@ -127,6 +127,18 @@
 
 
   @sect{Changelog}
+    @sect{3.0.0-M1}
+      @ul
+        @li
+          This release is not binary compatible with Ammonite 2.5!
+        @li
+          Support for Scala 2.12.18, 2.12.19, 2.13.11, 2.13.12, 2.13.13, 3.3.1, 3.3.2, 3.3.3
+        @li
+          The Scala 3 version now no longer depends on dependencies built with Scala 2.13
+        @li
+          Various dependency updates
+        @li
+          Internal fixes and improvements
     @sect{2.5.11}
       @ul
         @li
@@ -1759,7 +1771,7 @@
       generally work - the automated test suite is pretty comprehensive - but
       they are still more-likely to have bugs than numbered releases.
     @p
-      Any pull-request that gets merged into master is published as an unstable
+      Any pull-request that gets merged into the main branch is published as an unstable
       version automatically within an hour or two of being merged, so if you
       notice some problem and know how to fix it, send a PR, get it merged, and
       you can use the published unstable version with your fix until the next

readme/Scripts.scalatex

@@ -30,7 +30,7 @@
 
   @p
     As an example, Ammonite's own
-    @lnk("Continuous Integration Scripts", "https://github.com/lihaoyi/Ammonite/tree/master/ci")
+    @lnk("Continuous Integration Scripts", "https://github.com/lihaoyi/Ammonite/tree/main/ci")
     are written as @code{.sc} Scala Scripts, as are @lnk("Haoyi's blog",
     "https://github.com/lihaoyi/blog") and @lnk("resume",
     "https://github.com/lihaoyi/Resume"). These are all examples of using