fix unsigned warning in num_gmp_impl.h
Try to not leave secret data on the stack or heap.

This makes a basic effort and has not been audited.
Doesn't appear to have a measurable performance impact on bench.

It also adds a secp256k1_num_free to secp256k1_ecdsa_pubkey_create.
Make tests and bench just use asm directly instead of library

Thanks to Cory Fields for the suggestion.
Merge pull request #53

2f6c801 Try to not leave secret data on the stack or heap. (Gregory Maxwell)
Merge pull request #55

8881212 Make tests and bench just use asm directly instead of library (Pieter Wuille)
Add VERIFY_CHECK/DEBUG_CHECK and use CHECK macros more
Merge pull request #54

1c7fa13 Add VERIFY_CHECK/DEBUG_CHECK and use CHECK macros more (Pieter Wuille)
Merge pull request #51

364fde6 fix unsigned warning in num_gmp_impl.h (caktux)
Fix a signedness mistake in secp256k1_num_set_hex

We were using a potentially signed char as index in an array.
Merge pull request #56

fa492f0 Fix a signedness mistake in secp256k1_num_set_hex (Pieter Wuille)
Nothing-up-my-sleeving blinding for a*G
Only use the libcrypto part of OpenSSL
Merge pull request #58

3ed6dfa Only use the libcrypto part of OpenSSL (Pieter Wuille)
Merge pull request #57

62c3f55 Nothing-up-my-sleeving blinding for a*G (Pieter Wuille)
Make secp256k1_ge_set_gej work with the point at infinity
Merge pull request #62

1136bed Make secp256k1_ge_set_gej work with the point at infinity (Pieter Wuille)
Split up signing and verification initialization
Set precomputation table late and unset early.

Set the global pointer to the precomputation table only after initializing
it completely, and unset it before doing any uninitialization.

This causes fail-fast behavior in case of race conditions between
initialization and operations using it.
Merge pull request #60

c259a7c Set precomputation table late and unset early. (Pieter Wuille)
04e34d1 Split up signing and verification initialization (Pieter Wuille)
Make bench use external interface