Directory reorg: move code into redo/, generate binaries in bin/.

It's time to start preparing for a version of redo that doesn't work
unless we build it first (because it will rely on C modules, and
eventually be rewritten in C altogether).

To get rolling, remove the old-style symlinks to the main programs, and
rename those programs from redo-*.py to redo/cmd_*.py.  We'll also move
all library functions into the redo/ dir, which is a more python-style
naming convention.

Previously, install.do was generating wrappers for installing in
/usr/bin, which extend sys.path and then import+run the right file.
This made "installed" redo work quite differently from running redo
inside its source tree.  Instead, let's always generate the wrappers in
bin/, and not make anything executable except those wrappers.

Since we're generating wrappers anyway, let's actually auto-detect the
right version of python for the running system; distros can't seem to
agree on what to call their python2 binaries (sigh). We'll fill in the
right #! shebang lines.  Since we're doing that, we can stop using
/usr/bin/env, which will a) make things slightly faster, and b) let us
use "python -S", which tells python not to load a bunch of extra crap
we're not using, thus improving startup times.

Annoyingly, we now have to build redo using minimal/do, then run the
tests using bin/redo.  To make this less annoying, we add a toplevel
./do script that knows the right steps, and a Makefile (whee!) for
people who are used to typing 'make' and 'make test' and 'make clean'.

docs/fetchcode.js

@@ -0,0 +1,25 @@
+'use strict';
+
+async function fetchCode(e, lang, src) {
+    const resp = await fetch(src);
+    let t = await resp.text();
+    if (lang) t = hljs.highlight(lang, t).value;
+    e.innerHTML = t;
+}
+
+function fetchAndHighlightAll() {
+    const el = document.getElementsByTagName('code');
+    for (const e of el) {
+    	const src = e.getAttribute('src');
+    	if (!src) continue;
+    	const lang = e.getAttribute('lang');
+    	const title = document.createElement('b');
+    	title.innerText = src;
+    	title.style.textAlign = 'center';
+    	title.style.display = 'block';
+    	e.parentElement.insertBefore(title, e);
+    	fetchCode(e, lang, src);
+    }
+}
+
+setTimeout(fetchAndHighlightAll, 0);