Make .appveyor.yml into a branch-specific filename

The name should match the Appveyor account that builds the branch;
From a suggestion by Michael.

.appveyor.yml

@@ -1,144 +0,0 @@
-# .appveyor.yml for use with EPICS Base ci-scripts
-# (see: https://github.com/epics-base/ci-scripts)
-
-# branches to build
-branches:
-  # whitelist
-  only:
-    - 3.15
-    - /R3\.15\.\d+.*/
-
-# Version format
-version: base-{branch}-{build}
-
-#---------------------------------#
-#       build cache               #
-#---------------------------------#
-# The AppVeyor cache allowance is way too small (1GB per account across all projects, branches and jobs)
-# to be used for the dependency builds.
-
-cache:
-  - C:\Users\appveyor\.tools
-
-#---------------------------------#
-#       repository cloning        #
-#---------------------------------#
-
-# Called at very beginning, before repo cloning
-init:
-  # Set autocrlf to make batch files work
-  - git config --global core.autocrlf true
-
-# Set clone depth (do not fetch complete history)
-clone_depth: 5
-
-# Skipping commits affecting only specific files
-skip_commits:
-  files:
-    - 'documentation/*'
-    - '**/*.html'
-    - '**/*.md'
-    - '.github/*'
-
-#---------------------------------#
-#   build matrix configuration    #
-#---------------------------------#
-
-image: Visual Studio 2015
-
-# Build Configurations: dll/static, regular/debug
-configuration:
-  - dynamic
-  - static
-  - dynamic-debug
-  - static-debug
-
-# Environment variables: compiler toolchain, base version, setup file, ...
-environment:
-  # common / default variables for all jobs
-  SETUP_PATH: .ci-local:.ci
-  BASE: SELF
-  EPICS_TEST_IMPRECISE_TIMING: YES
-
-  matrix:
-  - CMP: vs2019
-    APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
-  - CMP: vs2017
-    APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
-  - CMP: vs2015
-  - CMP: vs2013
-  - CMP: vs2012
-  - CMP: vs2010
-  - CMP: gcc
-
-# Platform: processor architecture
-platform:
-  - x86
-  - x64
-
-# Matrix configuration: exclude sets of jobs
-matrix:
-  exclude:
-  # VS2012 and older installs don't have the 64 bit compiler
-  - platform: x64
-    CMP: vs2012
-  - platform: x64
-    CMP: vs2010
-  # Exclude more jobs to reduce build time
-  # Skip 32-bit for "middle-aged" compilers
-  - platform: x86
-    CMP: vs2017
-  - platform: x86
-    CMP: vs2015
-  # MinGW debug builds use the same libraries, unlike VS
-  - configuration: dynamic-debug
-    CMP: gcc
-  - configuration: static-debug
-    CMP: gcc
-
-#---------------------------------#
-#     building & testing          #
-#---------------------------------#
-
-install:
-  - cmd: git submodule update --init --recursive
-  - cmd: python .ci/cue.py prepare
-
-build_script:
-  - cmd: python .ci/cue.py build
-
-test_script:
-  - cmd: python .ci/cue.py test
-
-on_finish:
-  - ps: Get-ChildItem *.tap -Recurse -Force | % { Push-AppveyorArtifact $_.FullName -FileName $_.Name }
-  - cmd: python .ci/cue.py build test-results -s
-
-#---------------------------------#
-#         debugging               #
-#---------------------------------#
-
-## if you want to connect by remote desktop to a failed build, uncomment these lines
-## note that you will need to connect within the usual build timeout limit (60 minutes)
-## so you may want to adjust the build matrix above to just build the one of interest
-
-# print the connection info
-#init:
-#  - ps: iex ((new-object net.webclient).DownloadString('https://raw.githubusercontent.com/appveyor/ci/master/scripts/enable-rdp.ps1'))
-
-# block a failed build (until the watchdog barks)
-#on_failure:
-#  - ps: $blockRdp = $true; iex ((new-object net.webclient).DownloadString('https://raw.githubusercontent.com/appveyor/ci/master/scripts/enable-rdp.ps1'))
-
-#---------------------------------#
-#         notifications           #
-#---------------------------------#
-
-notifications:
-
-  - provider: Email
-    to:
-      - core-talk@aps.anl.gov
-    on_build_success: false
-
-  - provider: GitHubPullRequest