* Initial implementation of quintic extensions.
* Update to/from_biguint() methods.
* Draft of fast multiplication on quintic extensions over 64-bit base.
* cargo fmt
* Typo.
* Document functions (a bit).
* Refactor reduction step.
* Change multiplication call so that LLVM generates better assembly.
* Use one main accumulator instead of two minor ones; faster reduce.
* Use one main accumulator in square too; clean up redundant code.
* Call faster routines from Mul and Square impls.
* Fix reduction function.
* Fix square calculation.
* Slightly faster reduction.
* Clean up names and types.
* cargo fmt
* Move extension field mul/sqr specialisations to their own file.
* Rename functions to have unique prefix.
* Add faster quadratic multiplication/squaring.
* Faster quartic multiplication and squaring.
* cargo fmt
* clippy
* Alternative reduce160 function.
* Typo.
* Remove alternative reduction function.
* Remove delayed reduction implementation of squaring.
* Enforce assumptions about extension generators.
* Make the accumulation variable a u32 instead of u64.
* Add test to trigger carry branch in reduce160.
* cargo fmt
* Some documentation.
* Clippy; improved comments.
* cargo fmt
* Remove redundant Square specialisations.
* Fix reduce*() visibility.
* Faster reduce160 from Jakub.
* Change mul-by-const functions to operate on 160 bits instead of 128.
* Move code for extensions of GoldilocksField to its own file.
