restrictive version check limits usability of modified images

[maciejskorski]

With the current check of the image version format

toolkit/lib/shared-functions.sh

Line 13 in 0ae6584

if [[ ! "$IMAGE_VERSION" =~ ^([0-9]+)\.([0-9]+)\.([0-9])+(-RC[0-9]*)?(-with-texlive-full)?$ ]]; then

it is impossible to run images with custom tags (e.g. those committed with a user-chosen version).

Users would like flexibility on versioning , e.g. to 5.0.5-updated-tex