better error handling for office documents that don't contain a thumbnail image

prepared release of this branch

using internalmedia as rendering method for media thumbnails, now

more details on thumbnail generation criteria

added a note about the thumbnail's modification timestamp

VSCode Workspace is to be ignored

update to version infos

Add error handling for missing media files and update configuration messages (close #7)

added version history entry for v0.94

Release v0.94

Remove restriction on color space

Removed restriction on color space, see issue #6

/close #6

Updated info for release v0.93

Added title syntax for the thumbnail image

Text after the newly identified pipe is interpreted as title for the image.

Added support for pipe syntax in {{thumbnail>*}}

Close #5

corrected formatting and indentation

updated compatibility (added Igor)

Updated description of installation routine

Added my Dockerfile for easier dependency management

Prepared release of v0.92

Added checks for ImageMagick security policy issues

corrected table flaw

Prepared release v0.91

Thumbnail presentation is now defined via max-width and min-width

divided code into 3 php files

added reference PDF file for dependency checks