M42 release

New features:

• Separate library for computing the exact derivatives of Gram-Schmidt vectors: https://github.com/wedeling/Gram_Schmidt_Derivatives

Updates:

• Added non-linear activation possibility to deep-active subspace layer

Tutorials:

• 2 epidemiological deep-active subspace Jupyter notebook tutorials (HIV and COVID 19): https://github.com/wedeling/deep_active_subspace_data
• Jupyter notebook tutorial on use and validity the Gram-Schmidt derivatives: https://github.com/wedeling/Gram_Schmidt_Derivatives/blob/main/check_derivatives.ipynb