Squashed 'src/secp256k1/' changes from 8225239..84973d3

Squashed 'src/secp256k1/' changes from 8225239..84973d3

84973d3 Merge #454: Remove residual parts from the schnorr expirement.
5e95bf2 Remove residual parts from the schnorr expirement.
cbc20b8 Merge #452: Minor optimizations to _scalar_inverse to save 4M
4cc8f52 Merge #437: Unroll secp256k1_fe_(get|set)_b32 to make them much faster.
465159c Further shorten the addition chain for scalar inversion.
a2b6b19 Fix benchmark print_number infinite loop.
8b7680a Unroll secp256k1_fe_(get|set)_b32 for 10x26.
aa84990 Unroll secp256k1_fe_(get|set)_b32 for 5x52.
cf12fa1 Minor optimizations to _scalar_inverse to save 4M
1199492 Merge #408: Add `secp256k1_ec_pubkey_negate` and `secp256k1_ec_privkey_negate`
6af0871 Merge #441: secp256k1_context_randomize: document.
ab31a52 Merge #444: test: Use checked_alloc
eda5c1a Merge #449: Remove executable bit from secp256k1.c
51b77ae Remove executable bit from secp256k1.c
5eb030c test: Use checked_alloc
72d952c FIXUP: Missing "is"
70ff29b secp256k1_context_randomize: document.
9d560f9 Merge #428: Exhaustive recovery
8e48aa6 Add `secp256k1_ec_pubkey_negate` and `secp256k1_ec_privkey_negate`
2cee5fd exhaustive tests: add recovery module
678b0e5 exhaustive tests: remove erroneous comment from ecdsa_sig_sign
03ff8c2 group_impl.h: remove unused `secp256k1_ge_set_infinity` function
a724d72 configure: add --enable-coverage to set options for coverage analysis
b595163 recovery: add tests to cover API misusage
6f8ae2f ecdh: test NULL-checking of arguments
25e3cfb ecdsa_impl: replace scalar if-checks with VERIFY_CHECKs in ecdsa_sig_sign

git-subtree-dir: src/secp256k1
git-subtree-split: 84973d393ac240a90b2e1a6538c5368202bc2224