v0.8: Handle directory list JSON not containing file size or page count.

Handle directory list JSON not containing file size or page count.
(Looks like reMarkable removed this between 3.10 and 3.14 software.)
#1

• read_files() check for JSON keys before trying to read them.
• do_list() Dondt show size or page count if the directory list JSON
  didn't contain them.

v0.7: Added "download rmdoc" functionality

Added "download rmdoc" functionality

• added download_rmdoc()
• replaced '/', '', and ':' in visible names, with underscores
• moved PassThru() (prints byte counts while reading data from a file)
  from download_pdf.go to do_download.go, so other download_xxx() can
  use it
• included '-D' in usage() message

v0.06 - 2023-12-22

v0.06 - 2023-12-22

• Added download command
  • by UUID or by substring match in "VissibleName"
  • handles multiple substring match patterns
  • same "-1" handling for duplicate output files
• Added -c option to "flatten" folder structure
• Added "pattern searching" (UUID or filename substring) to list command
• Deprecated backup command, use download with no pattern instead
• Updated list command to do the same UUID/filename search as download
• Added -I option to set tablet IP address
  • only useful for tablets which have been "hacked" to make the web
    interface available over wifi or other interfaces