The linked list that hold modules were the biggest source of unsafe
string functions.  This change re-implements it in a more readable and
comprehensible way.  Also separates module functions in a file so it's
simpler to navigate through code.

This was a function from the original require, but it wasn't even
ever used there...

Also remove `expr.h` and `expr.c`, as well as associated test files (which weren't being used).

This reverts commit 068ec9ee.
loadIocsh is funcitonally equivalent to runScript

This reverts commit c6d3216a.

Should work now on all operating systems.