Add an x87 intrinsic version of a floor function
Improved the build versioning

Use "X87" to compile with x86 floating point intrinsics.
Use "DEF" to compile without any intrinsics.
x87 intrinsic version of a ceiling function
x87 intrinsic version of a truncation function
Replace usage of std.math with phi.core
Avoid the implicit conversion in the test
Can simplify the versioning system
x87 intrinsic version of a square root function
Updated the floor function

Now the function uses a template to convert to a certain numerical
type in the return value. When the result has an unsigned integral
type the input must be nonnegative.
Remove unnecessary extra code
Correspondingly update ceil and trunc
Reduce some unecessary versioning in abs
Use the new ceiling function in integer to avoid the cast
Merge pull request #132 from joichiro/i130

Implement a core API - version 1