emuR 2.2.0

new features / performance tweaks / improvements

• compete rewrite of hierarchical queries + requeries (now using CTEs) + clean-up of the EQL engine
• serve() -> save bundle performance bump due to SQLite transaction improvement + using prep. statements
• serve() function now downloads current release .zip instead of cloning repo to save time and bandwidth
• fixed a few more readr:: file vs path parameter warnings
• using readr::write_lines() function in export_TextGridCollection() to better support UTF-8 symbols
• added create_spectrogram_image_as_raster function that used the EMU-webApp
  JavaScript code to draw a spectrogram as a raster

bug fixes

• fixed invalid TextGrid export on empty levels