Support more complex comprehensions

[MarcMush]

fix #58, fix #267, fix #218

allows for comprehensions with conditions and multiple fors

also some refactoring:

• split showprogress_loop and showprogress_map out of showprogress
• remove a lot of useless ProgressMeter. in tests

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (807496a) 93.48% compared to head (1ba913a) 96.93%.
Report is 6 commits behind head on master.

Files	Patch %	Lines
src/ProgressMeter.jl	96.90%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #302      +/-   ##
==========================================
+ Coverage   93.48%   96.93%   +3.45%     
==========================================
  Files           1        1              
  Lines         399      555     +156     
==========================================
+ Hits          373      538     +165     
+ Misses         26       17       -9     

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