LuaRocks installation (Ubuntu Linux)

[Dirk Laurie <dirk.laurie@...>]

I have an opportunity to add LuaRocks from scratch on a machine that
did not yet have even Lua.

I did the following on an Ubuntu 16.04 laptop recently handed down to me:

1. Downloaded Lua 5.3.5 into a local directory, built it (I needed to
do that twice, installing libreadline-dev in between), installed it
(it goes to /usr/local by default).

2. Installed luarocks via the APT tool. This installs luarocks 2.2.0,
and also lua 5.1,
in /usr, not /usr/local.

It came as a bit of a shock that a two-year old distro still installs
5.1 as default lua.

3. Did 'luarocks install luarocks'. This installed luarocks 2.4.4-1.
Four executables with names starting 'luarocks' are now available:
luarocks            luarocks-5.1        luarocks-admin      luarocks-admin-5.1

4. 'luarocks install xml'. It also installed lfs and lub. All of them
to /usr/local. But 5.1 versions only.

Questions:

1. How do I get Luarocks to install 5.3 versions?
2. Can one install Luarocks 3.0.0 via an older Luarocks?