Add 'fixed' option to fix the position of progress bars

[mingrammer]

I've added fixed option to fix the position of progress bars. I think it is useful to make the position of multiple bars fixed while using multiprocessing.

With fixed option, you can fix the position of progress bars and make the bars keeping on its position even though a process was completed.

Real case

I wanted to run 8 jobs with 3 processes with multiprocessing. As you know, an order of job running is unexpectable, so it may be challenging to keep the progress bars for each job on its fixed positions.

1. leave=True (default) and using position

with tqdm(total=srcr.dbsize(), ascii=True, unit='keys', unit_scale=True, position=pos) as pbar:

Yes it is tracing option, so, unexpected process switching are all traced. So I can't fix progress bars on a single line for a process.

2. leave=False and using position

with tqdm(total=srcr.dbsize(), leave=False, ascii=True, unit='keys', unit_scale=True, position=pos) as pbar:

With leave=False, each progress bar will be updated on its (fixed) position. But, when a progress is completed, bars will be disappeared. So, I could not see completed output.

3. fixed=True and using position

with tqdm(total=srcr.dbsize(), fixed=True, ascii=True, unit='keys', unit_scale=True, position=pos) as pbar:

With fixed=True, I could see completed outputs which were not disappeared.fixed option is very simillar to leave=Fasle except that it does not "clear" the completed progress bar (at __exit()__).

[codecov-io]

Codecov Report

Merging #615 into master will decrease coverage by 0.41%.
The diff coverage is 57.14%.

@@            Coverage Diff             @@
##           master     #615      +/-   ##
==========================================
- Coverage   98.87%   98.45%   -0.42%     
==========================================
  Files           9        9              
  Lines         709      713       +4     
  Branches      127      129       +2     
==========================================
+ Hits          701      702       +1     
- Misses          5        6       +1     
- Partials        3        5       +2

[chengs]

I help you fix the error in travis-ci. If you find the perf test reports an error, try to rerun it in travis-ci. Sometimes it happens.

As to the decision of whether use this PR, let's wait @casperdcl to make it.

[mingrammer]

@chengs There seems no error in travis-ci

[chengs]

@mingrammer Ah, that's because I rerun the test in travis-ci. :-)

[mingrammer]

@chengs Ah, that's good! Thank you :)

[mingrammer]

Any progress?