Fix links in README.md.

Author: jimblandy

README.md

@@ -4,34 +4,34 @@ This program plots the Mandelbrot set and writes it out as a PNG file. It uses R
 
 Different commits show different implementation strategies:
 
-*   [Branch `single-threaded`](https://github.com/jorendorff/rust-mandelbrot/blob/single-threaded/src/main.rs)
+*   [Branch `single-threaded`](https://github.com/ProgrammingRust/mandelbrot/tree/single-threaded)
     is the base version of the program. It does all the work on the main
     thread.
 
-*   [Branch `bands`](https://github.com/jorendorff/rust-mandelbrot/commit/bands)
+*   [Branch `bands`](https://github.com/ProgrammingRust/mandelbrot/tree/bands)
     splits the plotting area up into eight bands, and assigns one thread
     to each.  This often makes poor use of the threads, because some
     bands take significantly longer than others to complete: once a fast
     thread completes its band, its CPU goes idle while its less
     fortunate brethren are still hard at work.
 
-*   [Branch `task-queue`](https://github.com/jorendorff/rust-mandelbrot/commit/task-queue)
+*   [Branch `task-queue`](https://github.com/ProgrammingRust/mandelbrot/tree/task-queue)
     gets an almost perfect linear speedup from its threads. It splits
     the plotting area up into many more bands, and then has threads draw
     bands from a common pool until the pool is empty. When a thread
     finishes one band, it goes back for more work. Since the bands still
     take different amounts of time to render, the problem cited above
     still occurs, but on a much smaller scale.
 
-*   [Branch `lockfree`](https://github.com/jorendorff/rust-mandelbrot/commit/lockfree)
+*   [Branch `lockfree`](https://github.com/ProgrammingRust/mandelbrot/tree/lockfree)
     uses Rust's atomic types to implement a lock-free iterator type, and
     uses that to dole out bands from the pool instead of a
     mutex-protected count. On Linux, this is no faster than the
     mutex-based version, which isn't too surprising: on Linux, locking
     and unlocking an uncontended mutex *is* simply a pair of atomic
     operations.
 
-*   [Branch `rayon`](https://github.com/jorendorff/rust-mandelbrot/commit/rayon)
+*   [Branch `rayon`](https://github.com/ProgrammingRust/mandelbrot/tree/rayon)
     uses the Rayon library instead of Crossbeam. Rayon provides a
     *parallel iterator* API that makes our code much simpler.  It looks
     a lot like Rust code that uses plain old iterators.