Add formatting options to format configuration

It seems that only raw values from the current version configuration sets can be output using the format string. When outputting times with single digit minutes this leads to timestamps that look like: "8:8" (8 minutes after eight).

It would be great if there were some options for simple variable transformations (like padding a variable with zeroes in this case). e.g.

{$timestamp.hour}:{$timestamp.minute|pl:0:2}

for padding from left to size 2 with zeroes etc.

Locate the format-string handling for current-version configuration and review how variables are rendered. Reproduce the single-digit-minute example, then define and test the requested padding option so a format such as {$timestamp.minute|pl:0:2} produces a two-character value.

Written by the indexing model from the issue text.