Mmap acquisition vi

[victorjonathanibanez]

This PR solves two issues combined (#36, #37):

• Added functionality and tests to subset to specific channels by indexing
• Added functionality and tests to subset to specific image region
• Added functionality to load data into memory-mapped array, that is stored under a path provided by the user (so it can manually be deleted afterwards)
• Changed data_start_offset & data_end_offset conditions such that empty acquisitions are allowed (but warning printed)

[codecov]

Codecov Report

Attention: Patch coverage is 78.84615% with 11 lines in your changes missing coverage. Please review.

Project coverage is 82.11%. Comparing base (6cf3c26) to head (4469fe8).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
readimc/mcd_file.py	78.84%	11 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #38      +/-   ##
===========================================
+ Coverage    80.77%   82.11%   +1.33%     
===========================================
  Files            9        9              
  Lines          619      643      +24     
===========================================
+ Hits           500      528      +28     
+ Misses         119      115       -4     

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