Create Linear Regression classes

[Squadula]

• [x] Linear Regression base class
• [x] Chaospy Linear Regression class
  • supported models:
    • [x] Monomials
    • [x] Hermite polynomials
    • [x] Legendre polynomials
• [x] Jupyter Notebook as API example: examples/fit/surrogate.ipynb (GP and LinReg)
• [x] integration test (mockup)
• [x] restructured Surrogate base class
  • moved pre_train, post_train and pre_predict from GaussianProcess to Surrogate
• [x] polishing for v0.5
  • clarified docs for Variables
  • added draft for new Components
  • set up pre-commit (black and nbconvert to clean notebooks, preparation for v0.6)

  • updated Contributing

    ToDo in a later PR:

• Sklearn & Custom Linear Regression class ?
• Fourier / Gaussian / Sigmoid basis transformers ?
• Bayesian Ridge ?
• optimize hyperparameters (sigma_n and sigma_p)
• Multi Output Regression
• unit tests

• documentation (& add example notebook to docs)

  Linear Regression with GORILLA data

→ it fits the data very well but can't model the ridge

[coveralls]

Pull Request Test Coverage Report for Build 2449712403

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 31 of 103 (30.1%) changed or added relevant lines in 6 files are covered.
• 58 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-1.8%) to 64.33%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
profit/sur/linreg/init.py	0	2	0.0%
profit/sur/sur.py	19	22	86.36%
profit/sur/linreg/linear_regression.py	0	9	0.0%
profit/sur/linreg/chaospy_linreg.py	0	58	0.0%
<!--	Total:	31	103	30.1%	-->

Files with Coverage Reduction	New Missed Lines	%
profit/sur/gp/gaussian_process.py	5	92.77%
profit/config.py	11	91.91%
profit/sur/sur.py	42	60.66%
<!--	Total:	58		-->

Totals
Change from base Build 2351568369:	-1.8%
Covered Lines:	2579
Relevant Lines:	4009

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💛 - Coveralls