Update Docs Theme

[wilwade]

Problem

Updating theme colors to the white/navy and mdbook to v0.4.42+

Steps to Verify:

1. cargo install mdbook@0.4.42
2. cd docs
3. mdbook serve

Want to also verify the generator?

1. cd tools/signed-request-generator
2. npm i
3. npm run build
4. cd ../..
5. rm -Rf docs/src/Generator && cp -a tools/signed-request-generator/build docs/src/Generator

Also did an npm audit fix on the library and generator tool

Screenshots (optional):

Light (New is on top):

Dark (New is on top):

Generator form (new on top):

[mattheworris]

• Skimmed through the changes
• Had to run the generator to get mdbook to serve
• Clicked through some pages to check colors
  🚢 it!