Estimated hours taken: 3
extras/complex_numbers/*:
Add an Mmakefile to build the complex number library, using the
new support for user-defined libraries.
Move the test cases into a new subdirectory `tests'.
Add a new subdirectory `samples', containing an example
module `fft.m' that uses the library.
Add a README file.
extras/complex_numbers/complex.m:
Add new functions `complex/1' (converts float to complex),
`cis' (cos + i * sin), and `conj'.
Rename `norm' as `abs2' (square of absolute value).
