Using Sparse Matrix LU to Decompose and Solve Equations

[H-Dynamite]

The use of sparse matrices can greatly improve simulation speed. This sparse matrix and sparse matrix LU decomposition are extracted from the EJML project and can be compatible with the GWT project. We hope to merge them into the project and make a contribution to open source development。

[pfalstad]

Linking to pull request:

https://github.com/SEVA77/circuitjs1/pull/17