Remove compute time

[emrysshevek]

Closes #202, #169, and #196.

• Adds a return_times flag (false by default) to determine whether to return compute times along with metafeature values or not.
• Removes compute times from test dataset metafeatures
• Put computation for X into a general resource computer so it can be timed
• Added note in docstring and README about the timing function

[codecov-io]

Codecov Report

Merging #203 into develop will decrease coverage by 0.17%.
The diff coverage is 80%.

@@             Coverage Diff             @@
##           develop     #203      +/-   ##
===========================================
- Coverage    92.54%   92.36%   -0.18%     
===========================================
  Files           13       13              
  Lines          751      760       +9     
===========================================
+ Hits           695      702       +7     
- Misses          56       58       +2

Impacted Files	Coverage Δ
...talearn/metafeatures/general_resource_computers.py	96.96% <100%> (+0.09%)	⬆️
metalearn/metafeatures/metafeatures.py	95.83% <71.42%> (-0.84%)	⬇️

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