Add no_std support

[MaulingMonkey]

This will require breaking changes.

Breaking Changes

• Custom error types (std::io::Error not available)
• Custom path types (std::path::Path not available for Library::load)
  • I could use abistr? Eliminates some edge cases?
  • Might need load_from_{path,str,cstr8,cstr16}?
  • load could trait-dispatch to one of the above?
• Allocation elimination (currently allocates to append \0 to paths)