Improve signing API documentation & specification #214

1. 
   sipa commented at 2:02 am on February 13, 2015: contributor

   Fixes #209.
2. sipa force-pushed on Feb 13, 2015
3. sipa force-pushed on Feb 13, 2015
4. Improve signing API documentation & specification 8030d7c0e5
5. sipa force-pushed on Feb 14, 2015
6. 
   sipa commented at 11:39 pm on February 14, 2015: contributor

   @gmaxwell done
7. sipa cross-referenced this on Feb 14, 2015 from issue secp256k1_ecdsa_sign: Added a warning about an infinite loop. by DavidEGrayson
8. 
   gmaxwell commented at 8:14 am on February 15, 2015: contributor

   ACK.
9. sipa merged this on Feb 16, 2015
10. sipa closed this on Feb 16, 2015

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11. sipa referenced this in commit 0bada0e2a9 on Feb 16, 2015

Contributors
sipa gmaxwell