Expose OpenSSL constant time bignum arithmetic (#4200)

* Expose BIGNUM constant time operations

This commit exposes the following functions:
BN_set_flags
BN_get_flags

BN_MONT_CTX_new
BN_MONT_CTX_set
BN_MONT_CTX_free

BN_mod_exp_mont
BN_mod_exp_mont_consttime

This commit also exposes the BN_FLG_CONSTTIME flag.

* Add myself to AUTHORS
2 files changed