Add Gaussian Noise Process submodule

[kdbarajas]

TODO::

• [ ] - Add unit test
• [ ] - Change CARMAProcess --> GaussianNoiseProcess
• [ ] - Add assertions/error codes for incorrect inputs or failures
• [ ] - Docstrings
• [ ] - Add examples
• [ ] - update docs to say import numpy and scipy in your python

[marwahaha]

more on submodules here: https://docs.julialang.org/en/v1/manual/modules/

[codecov[bot]]

Codecov Report

Merging #62 (08a2b3a) into master (e62be49) will decrease coverage by 12.8%. The diff coverage is 50.7%.

@@            Coverage Diff            @@
##           master     #62      +/-   ##
=========================================
- Coverage    92.3%   79.5%   -12.8%     
=========================================
  Files          15      23       +8     
  Lines        1165    1679     +514     
=========================================
+ Hits         1075    1334     +259     
- Misses         90     345     +255     

Impacted Files	Coverage Δ
src/noise/ARMA_NoiseProcess.jl	0.0% <0.0%> (ø)
src/noise/noisevector.jl	0.0% <0.0%> (ø)
src/noise/todo_noise_example_test.jl	0.0% <0.0%> (ø)
src/noise/Gaussian_types.jl	46.5% <46.5%> (ø)
src/noise/CARMA_NoiseProcess.jl	48.1% <48.1%> (ø)
src/lasers.jl	93.1% <80.0%> (-4.7%)	:arrow_down:
src/noise/Gaussian_interface.jl	85.7% <85.7%> (ø)
src/noise/ARMA_Structure.jl	88.0% <88.0%> (ø)
src/noise/CARMA_Structure.jl	93.5% <93.5%> (ø)
src/IonSim.jl	100.0% <100.0%> (ø)

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[marwahaha]

Goal after today: Make non-adaptive time-stepping the default

[marwahaha]

Two things from Joe:

• specify spectral density
• list of values (under the hood, turn it into a continuous function) #72