Update doc versions

INSTALL.txt

@@ -12,8 +12,8 @@ Quick Start

If you haven't already done so, extract the tarball:
 
    tar -x --xz < oil-0.5.alpha2.tar.xz
    cd oil-0.5.alpha2
    tar -x --xz < oil-0.5.alpha3.tar.xz
    cd oil-0.5.alpha3

Either install as /usr/local/bin/osh:

@@ -31,7 +31,7 @@ The latter doesn't require root access, but it requires ~/bin to be in your
PATH.

NOTE: Out-of-tree builds are NOT currently supported, so you have to be in the
oil-0.5.alpha2 directory.
oil-0.5.alpha3 directory.

Smoke Test
----------

doc/osh-quick-ref-toc.txt

@@ -2,7 +2,7 @@ OSH Quick Reference

- Below is a list of topics, organized into [Sections].
- The X prefix means "unimplemented".  Oil features are all unimplemented!
- HTML version: https://www.oilshell.org/release/0.5.alpha2/doc/osh-quick-ref.html
- HTML version: https://www.oilshell.org/release/0.5.alpha3/doc/osh-quick-ref.html

INTRO
  [Overview]      overview   osh-vs-oil   command-vs-expr

doc/release-index.md

@@ -1,6 +1,6 @@
<!-- NOTE: This file is at /release/$VERSION/index.html -->

Oil Version 0.5.alpha2
Oil Version 0.5.alpha3
-----------------

### What's New