Depends on #1346
Adds a module to the standard library to implement extension field
arithmetic. This should work and be correct on both the Goldilocks and
BN254 field. Needed for #1306.
---------
Co-authored-by: chriseth <chris@ethereum.org>
Allows braced blocks everywhere where expressions are expected.
The statements in those blocks can be `let x` or `let x = ...`.
The former declares a new witness column, the latter just binds a local
variable.
fixes#959
