SPRING code.
Part of this code come directly from a code that was given to us by Gaetan Leurent, one of the designer of SPRING-BCH and SPRING-CRT.

Contains:

- In fft_avx2 folder:
---> bch_ctr.c: SPRING-BCH code (from Gaetan Leurent) using AVX2 instructions.
---> common.c: set of functions that are common to both SPRING-BCH and SPRING-RS.
---> fft_bench.c and fft_bench32: timing of the fft.
---> new_ctr.c: SPRING-CTR code using AVX2 instructions.
---> test_fft32.c: set of test of various functions and macros.
---> vector.c: fft function and macros (using 8-coefficient vectors).
---> vector32.c: fft + rounding and rejection functions (using 16-coefficient vectors).
---> vector.h: set of macros for vector instructions.

- In spring_neon folder:
---> common.c: functions that are common to SPRING-BCH and SPRING-RS.
---> bch.c: SPRING-BCH for ARM-NEON instructions.
---> fft_bench: timing of the fft and of the BCH code.
---> rs.c: SPRING_RS for ARM-NEON instructions.
---> test_fft.c: set of test of various functions and macros.
---> vector.c: fft functions and macros.
---> vector.h: set of macros for vector instructions.