Rename import files to be just "sqimport".
Update includes after rename.
Rework logic to find module file:

Module is searched:
1) in current directory
2) in directory set by SQPATH environment variable
3) if that's not set, in $HOME/.squirrel/lib
4) if HOME is not set, in /usr/lib/squirrel

In each location, .nud, .nuc, .nut file is tried for binary,
bytecode, and source file respectively.
Rename low-level import function provide by this module to _import_().
Properly handle module not foun condition (throw exception).