lib: add testn impl

Signed-off-by: Fedor Indutny <fedor@indutny.com>
0.12.0
benchmarks: add Yaffle/BigInteger

Signed-off-by: Fedor Indutny <fedor@indutny.com>
benchmarks: a little refactor
lib: add gcd method
0.13.0
bn: add abs, iabs
bn: add failing tests for iaddn, isubn
Merge pull request #14 from dcousens/abs

Abs
Merge pull request #15 from dcousens/failadd

addn failing test
lib: fix infinite loop in gcd
lib: fix usage in browser
0.13.1
0.13.2