#4 Documentation of libraries in std_env

[Kenneth C. Schalk]

There should be a document saying what libraries are
available in the standard environment and generally
what is in each one.

There should probably also be a tool (maybe just an SDL
function) that looks through the result of building the
standard environment and lists the names of the
libraries that are available.

Perhaps we could combine these ideas. If libraries in
the standard environment included some descriptive
text, the tool that looks through the standard
environment could automatically generate a document
detailing the available libraries.