[block] add label and unit as optional args for array creation

[jgrewe]

No description provided.

[codecov-commenter]

Codecov Report

Merging #505 (3e225a4) into master (91df1f8) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #505      +/-   ##
==========================================
+ Coverage   78.74%   78.76%   +0.01%     
==========================================
  Files          59       59              
  Lines        9343     9351       +8     
==========================================
+ Hits         7357     7365       +8     
  Misses       1986     1986              

Impacted Files	Coverage Δ
nixio/block.py	73.28% <100.00%> (+0.17%)	⬆️
nixio/test/test_block.py	100.00% <100.00%> (ø)

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[coveralls]

Coverage increased (+0.02%) to 79.026% when pulling 3e225a4 on jgrewe:array_create into 91df1f8 on G-Node:master.

[achilleas-k]

These constructors are getting a bit unwieldy, but I suppose it's all optional so it's fine.

[jgrewe]

@achilleas-k when writing the example files for the python docs, the two lines to add unit and label were among the most annoying...
Closing and reopening to trigger appveyor