Start writing the aphid book

Cargo.toml

doc/.gitignore

doc/book.toml

doc/src/.gitignore

doc/src/SUMMARY.md

doc/src/example_config.toml

doc/src/install.md

doc/src/intro.md

doc/src/learn.md

doc/src/likelihood.md

doc/src/output.md

doc/src/preamble.mathjax

doc/src/preprocess.md

doc/src/use.md

src/bin/aphid/main.rs

src/bin/doc.rs

src/config.rs

src/config/check.rs

src/config/defaults.rs

src/config/raw.rs