v0.2.1

[Release note initially written by @madars and further modified by @ValarDragon]

This release merges #35 (thanks, @AntoineRondelet !) and thus slightly modifies the user-facing API, hence the version bump. We will refer to libff's v0.2.0 in libfqfft's and libsnark's v0.2.0.

Thank you to everyone who has contributed to libsnark/libff/libfqfft over the years!

This tag was previously known as 1.0, but was changed to 0.2.0 due to being unable to provide API stability guarantees.