Add bench_sign tool
Add verification to 32bit field

- implement _fe_verify for 10x26
- fe is normalized after _fe_clear
- a few corresponding changes in 64bit field
Better .gitignore for bench binaries
Merge pull request #83

7d681ac Add verification to 32bit field (Peter Dettman)
Merge pull request #82

8f9a307 Better .gitignore for bench binaries (Pieter Wuille)
fa5c13f Add bench_sign tool (Pieter Wuille)
Fix interaction between magnitudes and negation

Magnitude m means values are allowed to be up to 2 * 0xFFF...FFF * m,
while the argument passed to secp256k1_fe_negate didn't take the 2 into
account. Fix this.
Fix build for 64bit field under OSX

- caused by https://github.com/bitcoin/secp256k1/commit/8881212ebc43e67052ec06dec8beb459769fbab7
- OSX's ar tool doesn't work for empty archives ("ar: no archive members specified")
- introduce COMMON_LIB variable; leave empty when not using asm
Merge pull request #70

e2d66a2 Fix build for 64bit field under OSX (Peter Dettman)
Get rid of {num,scalar,ecdsa_sig}_{init,free}
Merge pull request #89

501d58f Get rid of {num,scalar,ecdsa_sig}_{init,free} (Pieter Wuille)
Merge pull request #85

7a8e385 Fix interaction between magnitudes and negation (Pieter Wuille)
Rewrite mul/sqr for 32bit/64bit

- interleave calculation of the lower and upper partial product ranges, and reduction
- less registers needed, more opportunities for parallel ops