This pre-release introduces an overhaul of the repository

• Set up GitHub actions runners
• Clean up build files which are set in .gitignore but are staged in the repo.
• Configure cmake to store executables and libraries in corresponding folders
• Setup testing environment
• Implement sample groups and compact sample groups in fragments
• Fix all compilation issues & warnings on macOS, linux and windows for libisomediafile
• Set up cmake to treat all warnings as errors (libisomediafile only)
• Implement defragmentation of the sampleToGroup and SampleGroupDescription boxes (merging etc.)
• Implement the API to change the flavour of the sample groups before writing a file.
• Implement an API to get the sample numbers given the sample group type and entry
• Implement a comprehensive sample group test
• Implement getDescriptionEntryCount to provide the API to iterate over
  all entries
• Implement an initial testing environment for sample description functions
• Clean up debugging output
• BugFix: allow multiple sample group descriptions of the same type to be present.
• BugFix: local compact sample groups in fragments
• BugFix: non mandatory tfdt
• BugFix: default local group description in fragments 0x10000 should be treated as 0
• BugFix: HEVC sample entry lengthSize-1 was not correctly written to file
• BugFix: get the correct value for the last sample number index
• Setup documentation of the API using doxygen and automate publishing it to gh-pages
• Setup clang-format and reformat all files in the libisomedia to have a unique style. Also automate checks for future pull requests.
• Switch HEVC reference software dependency from BBC to HHI as BBC server seems to be unreachable.