Update sin to use the X87 fp instrinsics when available
Use X87 intrinsics for cos when available

The previous value was -0.416155 which is incorrect in the last two
digits as the correct value is -0.4161468365 to ten significant
digits. As of this commit, the value for cos(2.0) is -0.416147.
Use X87 intrinsics for tan when available
Improved the header for tan and added a contract
Added a contract for cosine
Update arctan to use the X87 fp instrinsics when available
Use X87 instrinsics for lb (log base 2) if available
Added contracts to ln and lg
Updated ln and lg to be based on lb
Standardize the inline assembly formatting
Merge pull request #127 from joichiro/i126

Use X87 intrinsics for elementary functions when available