Minor cleanup in Source::Diffview, and no longer unnecessarily locks parse_mutex before updating tags

Removed Arch Linux AUR package instructions, since users are reporting memory issues due to tmpfs being used by makepkg

Language protocol: use default settings of the rust language server. didChangeConfiguration has to be sent though, for some reason, or else the rust language server will not respond to all supported request types.

Language protocol: do not overwrite format_style when Prettier can be used on javascript/typescript files

Improved speed of directory view when opening folder containing a large number of files or directories

Cleanup and fixes to dialog and tooltip positioning. Dialogs and tooltips should now not be partially shown outside of screen

Language protocol: now shows possible arguments if no argument info is sent from server after autocomplete

Notebook::open() parameter cleanup, and removed unnecessary while(Gtk::Main::events_pending()) loops

Fixed threaded dispatcher disconnects that must happen in the main thread. Also fixed potential crash when full reparse is needed before exiting juCi++

Fixed usage cache count, simplified Gtk::Main::iteration calls, and added info message about background processes if any when quitting juCi++

Improved snippets: now supports variables TM_SELECTED_TEXT, TM_CURRENT_LINE, TM_CURRENT_WORD, TM_LINE_INDEX, TM_LINE_NUMBER, TM_FILENAME_BASE, TM_FILENAME, TM_DIRECTORY, TM_FILEPATH, CLIPBOARD, and default values. Binding shortcuts to snippets is also possible by adding key values in snippets.json

Improved entry history that is for instance used in the search dialog. Can now go to previous text history, and back to last written text

Added preferences item debug_place_cursor_at_stop to update cursor when the debugger stops as suggested in #252