Add MacPorts default include/lib paths for OSX
secp256k1_fe_sqrt checks for success

- secp256k1_fe_sqrt now checks that the value it calculated is actually a square root.
- Add return values to secp256k1_fe_sqrt and secp256k1_ge_set_xo.
- Callers of secp256k1_ge_set_xo can use return value instead of explicit validity checks
- Add random value tests for secp256k1_fe_sqrt
Use endomorphism in precomputations
Documented autotools build process in readme
Support 64bit_asm field on OSX
Merge pull request #23

17eec03 Support 64bit_asm field on OSX (Peter Dettman)
Merge pull request #22

7fc1fb4 Documented autotools build process in readme (John Driscoll)
Merge pull request #20

d7fd4d0 Use endomorphism in precomputations (Peter Dettman)
Merge pull request #19

09ca4f3 secp256k1_fe_sqrt checks for success (Peter Dettman)
Merge pull request #17

a86f241 Add MacPorts default include/lib paths for OSX (Peter Dettman)
Merge branch 'master' of https://github.com/bitcoin/secp256k1 into faster-64bit-normalize