Fixed #306: llvm assertion fail when casting nil to Void*. Also: allow casting nilable type to Void* (wasn't working).

Organized math dir and removed unecessary if-else for gamma in libm

Remove trailing whitespace

Use `require "http/client"`, `require "http/server"` instead of `require "net/http"`... Related to #279

String#split(separator : Regex)

Set default whence in FileDescriptorIO#seek to SEEK_SET.

Added C::PtrDiffT alias and did housekeeping of C types

add set clear