Finishing the Function Reference Documentation

This release adds a few bits of functionality and finally completes the standard library
reference documentation. All standard library functions have now at least a small
note and/or example to show how to use it. You can read the documenation
here: https://docs.rs/wlambda/newest/wlambda/prelude/index.html#wlambda-reference

• Incompatible Change: Renamed std:io:file:copy to std:fs:copy.
• Incompatible Change: Renamed error_to_str to std:error_to_str.
• Documentation: Completed standard library function reference documentation.
• Feature: std:rand :i64 now returns an integer in the full i64 range.
• Feature: Implemented slicing operations for calling pairse and integer vectors
  with vectors and iterators.