* guix/import/pypi.scm (python->package-name, maybe-inputs, compute-inputs,
guess-requirements): New procedures.
* guix/import/pypi.scm (guix-hash-url): Now takes a filename instead of an
URL as input.
* guix/import/pypi.scm (make-pypi-sexp): Now tries to generate the inputs
automagically.
* tests/pypi.scm: Update the test.
* guix/import/cabal.scm: New file.
* guix/import/hackage.scm: Update to use the new Cabal parsing module.
* tests/hackage.scm: Update tests.
* guix/scripts/import/hackage.scm: Add new '--cabal-environment' and '--stdin'
options.
* doc/guix.texi: ... and document them.
* Makefile.am (MODULES): Add 'guix/import/cabal.scm',
'guix/import/hackage.scm' and 'guix/scripts/import/hackage.scm'.
(SCM_TESTS): Add 'tests/hackage.scm'.
Fixes compilation failures in 'guix pull'.
* guix/import/cpan.scm (%corelist): Change it to a promise by wrapping it with
'delay'.
(cpan-module->sexp): Adapt uses of %corelist by wrapping with 'force'.
* guix/snix.scm: Delete.
* guix/import/snix.scm: New file.
* guix/import/pypi.scm: New file.
* guix/import/utils.scm: New file.
* guix/scripts/import/nix.scm: New file.
* guix/scripts/import/pypi.scm: New file.
* tests/pypi.scm: New file.
* tests/snix.scm: Import (guix import snix) module.
* guix/scripts/import.scm (%default-options, %options): Delete.
(%standard-import-options, importers): New variables.
(show-help): List importers.
(guix-import): Factor out Nix-specific logic. Delegate to correct importer
based upon first argument.
* configure.ac (HAVE_GUILE_JSON): New conditional.
* Makefile.am (MODULES): Add new files and remove 'guix/snix.scm'.
(SCM_TESTS): Add 'tests/pypi.scm' if guile-json is installed.