Rename master to main and update news

Update CI and README to reflect rename.
Update News:
    * Notify users of rename.
    * Update minimum required VS compiler to 2019.
    * Remove notice about versioning. This has been completed.
    * Remove notice about SPIRV folder relocation. It has been 2.5 years
    since this occured.

.appveyor.yml

@@ -15,7 +15,7 @@ configuration:
 
 branches:
   only:
-    - master
+    - main
 
 # changes to these files don't need to trigger testing
 skip_commits:
@@ -31,9 +31,9 @@ skip_commits:
     - Android.mk
     - _config.yml
 
-# Travis advances the master-tot tag to current top of the tree after
-# each push into the master branch, because it relies on that tag to
-# upload build artifacts to the master-tot release. This will cause
+# Travis advances the main-tot tag to current top of the tree after
+# each push into the main branch, because it relies on that tag to
+# upload build artifacts to the main-tot release. This will cause
 # double testing for each push on Appveyor: one for the push, one for
 # the tag advance. Disable testing tags.
 skip_tags: true
@@ -73,7 +73,7 @@ after_test:
       }
   - cd install
   # Zip all glslang artifacts for uploading and deploying
-  - 7z a glslang-master-windows-"%PLATFORM%"-"%CONFIGURATION%".zip
+  - 7z a glslang-main-windows-"%PLATFORM%"-"%CONFIGURATION%".zip
     bin\glslangValidator.exe
     bin\spirv-remap.exe
     include\glslang\*
@@ -97,12 +97,12 @@ deploy:
   - provider: GitHub
     auth_token:
       secure: YglcSYdl0TylEa59H4K6lylBEDr586NAt2EMgZquSo+iuPrwgZQuJLPCoihSm9y6
-    release: master-tot
-    description: "Continuous build of the latest master branch by Appveyor and Github"
+    release: main-tot
+    description: "Continuous build of the latest main branch by Appveyor and Github"
     artifact: artifacts-zip
     draft: false
     prerelease: false
     force_update: true
     on:
-      branch: master
+      branch: main
       APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015