add custom output for the ToString() function

[wzx1996]

Overrided the ToString() function to let it output the matrix/vector in the format of MATLAB matrix. This is mainly for debugging purpose, as it would be easier to check the value from the watch window or output the value to the debug log.

Also, it might be useful if you want to export the matrix/vector to another program, but this is not the intended usage.

The main reason I want to have this feature is, I'm tired of expanding the structure to check the value while debugging in Visual Studio. With this, I won't have to expand the structure to check all the value.

[codecov[bot]]

Codecov Report

Merging #7 into master will decrease coverage by 1.19%. The diff coverage is 37.55%.

@@            Coverage Diff            @@
##           master       #7     +/-   ##
=========================================
- Coverage   32.42%   31.22%   -1.2%     
=========================================
  Files          10       10             
  Lines         549      570     +21     
=========================================
  Hits          178      178             
- Misses        371      392     +21

Impacted Files	Coverage Δ
source/GlmNet/GlmNet/mat4.cs	64% <26.31%> (-6.59%)	:arrow_down:
source/GlmNet/GlmNet/vec2.cs	28.57% <28.57%> (-0.85%)	:arrow_down:
source/GlmNet/GlmNet/mat3.cs	29.85% <32.55%> (-2.94%)	:arrow_down:
source/GlmNet/GlmNet/mat2.cs	41.93% <41.86%> (-3.68%)	:arrow_down:
source/GlmNet/GlmNet/vec3.cs	43.18% <43.18%> (-1.01%)	:arrow_down:
source/GlmNet/GlmNet/vec4.cs	44.44% <44.44%> (-1.02%)	:arrow_down:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update cd1cd42...2ac1724. Read the comment docs.

[dwmkerr]

Nice! Thanks @wzx1996 and sorry for the delay, lost track of this project, coming back to it now