Add 'pre-commit' framework

This pull request adds a basic pre-commit configuration to the repository and runs the check in a CI step.

This configuration does the following:

check-added-large-files: prevent accidental adding of large files
check-case-conflict: prevent that files being added that cause problems on NTFS/Windows.
check-executables-have-shebangs: If file is marked executable, it shall have a shebang.
check-merge-conflict: do not add files, that have conflict markers
check-shebang-scripts-are-executable: if a file has a shebang, then it should be marked as executable
check-symlinks: symlinks shall point to anything meaningful
check-yaml: yaml files shall be valid yaml files
destroyed-symlinks: prevent symlinks getting converted to files (mostly a Windows thing)
end-of-file-fixer: POSIX 3.206 Line
fix-byte-order-marker: removes UTF-8 byte order marker (mostly a Windows thing)
mixed-line-ending: do not mix LF/CR/CRLF in a file
trailing-whitespace: do not use trailing whitespace (except for MarkDown files)

Let's make diffs smaller and reviews simpler :)

Actual changes by this commit: all changes are cosmetic except for

the following files that were marked executable, but had no shebang:
- plugins/beep/lib/beep.rb: added ruby shebang
- plugins/bullseye/bullseye.rake: added ruby shebang
- plugins/bullseye/lib/bullseye.rb: added ruby shebang
- plugins/command_hooks/lib/command_hooks.rb: added ruby shebang
- plugins/gcov/gcov.rake: added ruby shebang
- plugins/gcov/lib/gcov.rb: added ruby shebang
- plugins/module_generator/lib/module_generator.rb: added ruby shebang
- plugins/module_generator/module_generator.rake: added ruby shebang
the following files had a shebang, but were not marked executable:
- Rakefile: now marked as executable
- examples/temp_sensor/test/support/UnityHelper.h: removed executable bits
- plugins/bullseye/config/defaults.yml: removed executable bits

ThrowTheSwitch / Ceedling