Allow forcing the progress bar update

[alyst]

The PR adds the force=true/false keyword argument to updateProgress!() method.
When force=true, the progress bar is unconditionally updated regardless the too frequent bar updates check.

The use case: I am processing the big data file that I download chunk by chunk (one chunk contains thousands of data entries).
The progress bar reflects how many entries have been processed.
Each datum is processed within fraction of a second.
However, downloading the next chunk of data takes a while (minutes), during which time the progress bar freezes.
I use showvalues= to report the current status: either data processing or chunk download.
The problem is that in 99.9% cases the download-related progress bar update gets suppressed by the frequency filter (dt) -- so during the download the bar incorrectly reports that data entries are being processed.
So with this PR I can make sure that the bar would be updated just before the download by passing force=true.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.77%. Comparing base (807496a) to head (221e735).
Report is 14 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #315      +/-   ##
==========================================
+ Coverage   93.48%   96.77%   +3.29%     
==========================================
  Files           1        1              
  Lines         399      558     +159     
==========================================
+ Hits          373      540     +167     
+ Misses         26       18       -8     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[MarcMush]

Does dt=0 not work in this case?

[alyst]

Does dt=0 not work in this case?

It should definitely update the bar at each step, but that's not what I want:
I have ~10^8 fast steps and ~20 slow steps, and dt logic is perfectly fine for the small steps to avoid flooding the terminal.
I only want to make sure that the bar is updated for each slow step.

[MarcMush]

indeed it makes sense
I thought update!(p;dt=0) would work but it doesn't