Rework CI workflows (#8688)

- split workflows into separate files to trigger by path
  this should help out documentation and boards / eboot / pkg files
  updates, since those *wont* trigger usual build stuff anymore
- build*.sh whatever merged into just common.sh and build.sh
  trigger different parity builds, mod % rem and allow to set .ino list
  through the environment variable
- removes unnecessary temporary files, try to use more pipes
  move remaining ones into cache dir instead of PWD
- remove legacy TRAVIS env vars, use ESP8266_ARDUINO prefix for config
- remove Windows path workarounds
- hardware/ and ide/ directories are set through envionment
  do not force specific paths, simplify builds on local machine
- sketch list is set through environment. expicit paths for Windows and
  macOS builders. platformio also gets a real shuffled list instead of
  mod and rem magic numbers
- detect root of the repo through git cli, not base{name,dir} or relative paths

tests/ci/build_docs.sh

@@ -4,6 +4,5 @@
 
 set -ev
 
-cd $TRAVIS_BUILD_DIR/doc
-
-SPHINXOPTS="-W" make html
+root=$(git rev-parse --show-toplevel)
+env SPHINXOPTS="-W" make -C $root/doc html