Clean up residual and linearization

[mrp089]

Closes #53.

Code changes:

• Cleaned up residual and linearization as described in #53
• Add output for average number of Newton iterations per time step

Documentation:

• Adapted documentation to new formulation
• Added documentation from simvascular.github.io

Testing:

• Same results
• Same number of Newton iterations
• Same runtime (should be a tiny bit faster now)

[mrp089]

I also changed our LaTeX rendering to MathJax since it looks nicer. However, this got me into a rabbit hole:

• MathJax only supports a couple of LaTeX packages. We use CircuiTikZ package for the schematics of 0D blocks, which is not supported.
• I thus compiled all schematics and saved them under docs/png, one for light mode and one for dark mode
• GitHub markdown allows switching images by toggling light/dark mode. However, this feature is (currently) not supported in Doxygen.

I thus defaulted to the dark version of each schematic. I think that's fine since it's still readable in light mode, and we also have only one light mode in our current documentation. Maybe in a future version of Doxygen we can include an automatic switch.