* guix/gexp.scm: New file.
* tests/gexp.scm: New file.
* Makefile.am (MODULES): Add guix/gexp.scm.
(SCM_TESTS): Add tests/gexp.scm.
* doc/guix.texi (Derivations): Add #:inputs in 'derivation' example.
Mark 'build-expression->derivation' as deprecated, refer to
"G-Expressions". Remove paragraph about code strata.
(G-Expressions): New node.
Ludovic Courtès